merely doubling oxygen, sulphur, selenium, and carbon, in the then existing system of atomic weights in the hydrogen scale, he really introduced a system in which there are between 30 and 40 atomic weights to correct, in lieu of one which needed only five or six such corrections. It would be unreasonable to apply this fact in any degree to the disparagement of Gerhardt's work. It only shows how tortuous is the road which leads to truth. The discussion of the question involves chiefly the consideration of the classification of the elements under the respective heads of chlorine and of oxygen. The first tribe containing those elements of which an atom combines with one atom of hydrogen or chlorine, or with three or with five, &c., whilst the second tribe contains elements of which each atom combines with two atoms of chlorine, or other monads, or with four, or six, &c. The speaker did not, however, recommend that the two great classes of elements be thus distinguished from one another, for our chief evidence of atomic weights is derived from the study of the molecular weights of compounds, and the molecule is the unit to which results must be referred. = The first class is best described as furnishing only an even number of atoms to each molecule, whereas the second class sometimes furnishes an even, sometimes an uneven, number of atoms to one molecule. The process of classifying the elements has followed the very natural order of establishing a certain number of well-defined families, which were subsequently connected together by erratic members, which occasionally left their usual place to go over to some neighbouring family. Chlorine, bromine, and iodine have long been acknowledged to constitute a natural family; and there are some, though hardly sufficient, reasons for placing fluorine at its head. The three elements have the same vapour volume as hydrogen in the free state, and we accordingly represent their respective molecules as Cl2,Br2,I2, corresponding to H2 2 vols. They form hydrides of similar composition, and analogous properties, and of the same vapour volume. Their com pounds with most metals are analogous, and have the same atomic heat and general crystalline form. Their corresponding oxygen acids also exhibit considerable analogy. With organic radicals they form neutral ethers, like CIC2H, CIC2H2O, and no acid ethers. So that when a molecule of alcohol or of acetic acid is replaced by chlorine, two atoms of chlorine take the place of one atom of oxygen, and give rise to a molecule of chloride of ethyle and a molecule of hydrochloric acid. They replace hydrogen atom for atom, taking out one, two, or three atoms, &c., according to circumstances. Their hydrogen compounds are all monobasic acids; for if, in a given quantity of hydrochloric or hydrobromic or hydriodic acid, we replace part only of the hydrogen by potassium, we get at once a neutral salt mixed with the remaining acid, which is undecomposed, and never an acid salt of the alkalies. Fluorine in this respect exhibits an anomaly which tends to remove it from this family to a biatomic one. For the acid fluoride of potassium is a well-defined compound of considerable stability, of which the existence points to the atomic weight 38 for fluorine, and the formula HF for hydrofluoric acid. Hydrofluoric acid, moreover, combines with various metallic fluorides-such as fluoride of silicon and fluoride of boron; and there are double fluorides of aluminium, &c., with alkaline fluorides, both well known and easily formed. Similar double salts are, however, formed by chlorine; for instance, terchloride of gold combines with a molecule of hydrochloric acid, or of an alkaline chloride. Tetrachloride of platinum combines with two molecules of hydrochloric acid or of chloride of potassium, &c. It is not possible to reconcile the constitution of these and similar bodies with one another and with the simpler compounds of chlorine, by any theory representing it as polyatomic, and as holding together the metallic atoms in these salts in virtue of its polyatomic character. On the other hand, hydrochloric acid and metallic chlorides of opposite properties cannot be assumed to be incapable of uniting with one another, while it is well known that oxides of basylous properties unite with those of chlorous properties. Hydrochloric acid unites with ammonia, and we do admit that the two molecules are bound together into one by a chemical force of combination, and not by any tetratomic character of the hydrogen; and HCl or KCl combines, with SO, by a similar force. Again: oxygen, sulphur, selenium, and tellurium are admitted to be truly analogous elements, for the parallelism of oxygen salts, and sulphur salts, affords abundant proof of the analogy of oxygen and sulphur, and the molecular volume of sulphur and selenium is found by Deville to agree at high temperatures with that of oxygen. The elements selenium and tellurium form acids analogous to sulphurous and sulphuric acids respectively. When combined with organic radicals they form compounds of the same molecular volume in the form of vapour; and when any of them, such as oxygen, replaces hydrogen in an organic body, it takes out two atoms of hydrogen at a time, replacing each couple by one atom of oxygen, as in the formation of acetic acid from alcohol. When we partially decompose water by potassium we get hydrate of potash formed, which is a molecule of water, from which half the hydrogen is expelled and replaced by potassium, and a second atom of potassium is required to displace the remaining hydrogen. If we compare any proto-chloride with a corresponding oxide, either of a metal or organic radical, we find that the molecule of the oxide contains twice as many atoms of the metal or radical as the chloride, and that one atom from the oxygen family is equivalent to two atoms from the chlorine family. When oxygen in alcohol is replaced by sulphur, no breaking up into sulphide of ethyle and sulphide of hydrogen takes place, as when the oxygen is replaced by chlorine or bromine. Among the best known compounds there are several of which one atom combines, like an atom of oxygen or of sulphur, with two atoms like hydrogen or chlorine. This carbonic oxide, sulphurous acid, and olefiant gas are capable of combining in the proportion of one atom of the radical with two atoms of chlorine, forming the compound CO Cl, phosgene, So, Cl2 chloro-sulphuric acid, and C,H,CI, Dutch liquid; and these molecules have the same vapour volume as steam OH2. But in the free state the radicals have a vapour volume double as great as the equivalent quantity of oxygen, the atoms CO,SO2,C2H4 being as bulky as O2, so that whereas the molecule of oxygen and of sulphur consists of two atoms, that of carbonic oxide consists of one atom only, so also the molecule of sulphurous acid and of olefiant gas. Another family of very marked characteristics is that consisting of N,P,As, Sb, Bi, each member of which combines with three atoms of hydrogen or of ethyle (CHS), forming basic compounds analogous to ammonia. Their analogy in chemical reactions is also well known, as each of them forms an oxide corresponding to nitrous acid, and another corresponding to nitric acid. The sulphides of arsenic and antimony are notorious for their great resemblance, and that of arsenious and antimonious acid is scarcely less striking. It even extends to isomorphism of their corresponding salts. The atomic heat of the four last terms of the series is also very nearly the same, whilst that of nitrogen (examined of course as a gas) is considerably less. Then the molecule of phosphorus and of arsenic consists of four atoms, whilst that of nitrogen consists only of two, showing a variety of constitution which is by no means to be wondered at, when we recollect that these elements are not uniformly triatomic, but sometimes monatomic, pentatomic, &c., so that the molecule of free nitrogen consists 52 Royal Institution of Great Britain. of two monatomic atoms, or two triatomic, whilst the molecule of phosphorus and of arsenic is formed on the ammonia type of one triatomic atom and three monatomic atoms. Another family may, perhaps, be made up of carbon and silicon, both of which form volatile tetrachlorides, and are sometimes biatomic, sometimes tetratomic in their acids. Among metals, lithium, sodium, potassium, and probably also the new metals rubidium, cæsium, and thallium, have many important points of resemblance which show them to be monatomic. They replace hydrogen atom for atom, and form with many bibasic acids both normal and acid salts. Their chlorides form with tetrachloride of platinum analogous double salts, and their sulphates form, with sulphate of alumina, &c., those well-characterised salts called alums. They do not form basic salts (unless when triatomic, like thallium). They have nearly the same atomic heat. Silver is remarkable for several of the properties which we have noticed in the alkali metals. It is eminently monatomic, and disinclined to form basic salts. Its atomie heat also shows it to be monatomic. It appears to form an alum, and its sulphate has a great resemblance of form with the anhydrous sulphate of soda. Gold also must, from its specific heat and the constitution of its two chlorides, be classed among the metals which are monatomic or triatomic. Boron is evidently triatomic in its best known compounds, as proved by the terchloride and ethylide. Among metals with strongly basylous properties, Ca, Sr, Ba, Pb, are connected by very close analogies. The general resemblance of their sulphates and carbonates, and the ismorphism of most of them, are too well known to need mention. But lead has been obtained in combination with ethyle, and the compound Pb(CH), which corresponds to binoxide of lead, in which the two atoms of oxygen are replaced by four atoms of ethyle, and the compound Pb(CH) Cl proves beyond a doubt that the metal is there tetrabasic. Again lead is pre-eminent for its tendency to form basic salts even with purely monatomic chlorous elements and radicals. Thus ordinary nitrate of lead, when warmed in aqueous solution with ceruse, expels carbonic acid from that compound, and forms the well-known and crystallisable basic nitrate July 30, 1864. and to represent their oxides by the old formulæ CaO, BaO, PbO, whilst carbonates, sulphides, and sulphates have formulæ like CaCO,, CaSO,, CaSO, their chlorides, nitrates, and phosphates have formulæ like CaCl2, Ca(NO3)2, Ca,(PO4)2. Nitrate of potash has thus a similar formula (NOK) to arragonite CO,Ca, and their isomorphism is no longer surprising. The same remark applies to calc spar and nitrate of soda. Another analogous group of metals is the triad, magnesium, zinc, and cadmium, all volatile and forming salts which greatly resemble one another, and in many cases isomorphous. The constitution and properties of Frankland's zinc ethyle leaves no doubt of the biatomic character of zinc, for the compound Zn(CH), has the same molecular volume as ether O(CH)2, and if the atom of zinc were taken out and replaced by one atom of oxygen, there would be no change of volume. Then half the ethyle in zinc ethyle is replaceable by iodine, just as half the ethyle in ether is replaceable by potassium. The biatomic character of this family being thus estabiished, we can extend the conclusion to the other metals which form magnesian oxides, so called from the striking analogy of constitution of several of their salts with the corresponding salt of magnesia. In this manner we are led to adopt for iron, manganese, nickel, cobalt, and copper atomic weights corresponding to biatomic characters. The subsulphide of copper is thus represented by the formula Cu2S, which is sufficiently similar to that of sulphide of silver, AgS, to remove Our surprise at their isomorphism. There is, moreover, in the reactions of alumina, sesquioxide of iron, sesquioxide of chromium, and sesquioxide of manganese, much resemblance. All these are weak bases, and their sulphates form with sulphate of potash those most characteristic salts called alums. The three first are isomorphous in the uncombined state, so that the conclusion established for iron and manganese may be extended to aluminium and chromium. But it is also arrived at by other means, for chromium in combination with oxygen and chlorine forms the well-characterised compound CrO2Cl2 chloro-chromic acid, which contains the same quantity of oxygen and of chlorine as chloro-sulphuric acid in two volumes of vapour, having 52.5 of chromium in the place of the 32 of sulphur of that compound. Again, chromic and sulphuric acids exhibit a marked resemblance of properties, the former being, if anything, even more distinctly bibasic than the latter, and their normal potash salts are isomorphous, so that chromium is abundantly proved to be similar to sulphur in atomicity, If this be represented upon the water type, it is formed and brings in evidence of its own in favour of the biatomic from two molecules of water But if the binary theory be adopted, it must be represented as lead combined with the radical NO,, and also with the radical HO, and the biatomic lead holds thus two atoms together, just as much as biatomic oxygen holds together ethyle and hydrogen in alcohol. If we mix our lead compound with sulphate of silver, and heat with water, we replace the one atom of lead in it by two atoms of silver, getting a mixture of nitrate of silver and brown hydrated oxide of silver, just as the replacement of oxygen in alcohol by Cl, forms chloride of ethyle + hydrochloric acid. We are thus led to consider these metals as biatomic, character of aluminium, iron, and manganese. In like manner manganese in manganic acid is connected with sulphur in sulphuric acid, and requires a corresponding biatomic weight. The isomorphism and general analogy of permanganate of potash with perchlorate of potash has often been alluded to as pointing to the necessity of representing the former by a formula containing one large atom of manganese, MnO,K: but although this formula, by assimilating the expressions for these two similar bodies, removes one difficulty, it creates at the same time another difficulty, by presenting a formula containing only one atom from the first family of elements. The speaker said he would not at present hazard any opinion regarding the propriety of removing this difficulty by doubling the above formule, together with that of perchlorate of potash, although he might remark that the constitution of the basic per-iodate of soda points to the formula I2O,Na, 3 (H2O). a An exceedingly strong ground for admitting for many heavy metals the atomic weight corresponding to biatomic character was brought forward some time ago by Wurtz, who pointed out that adopting for oxygen the atomic weight 16, we get a half-molecule of water H2O 2 CHEMICAL NEWS, Royal Institution of Great Britain-Cantor Lectures. in one molecule of various salts if we consider the heavy metals monatomic. Other metals are susceptible of reduction by similar analogies to the class of elements which are biatomic or tetratomic, &c. Thus mercury is proved by the ethylide and methylide to be biatomic by the fact that the compound for one atom of mercury with two atoms of ethyle or of methyle, occupies the same volume in the state of vapour as the compound of one atom of oxygen with two of ethyle or of methyle Hg(CH3)2= 2 vols., and we can take out one atom of methyle from the bi-methylide of mercury, and replace it by an atom of chlorine, bromine, or iodine without disturbing the type, CH3 Hg. a The common bi-chloride of mercury has, moreover, vapour volume corresponding to the biatomic character of the metal, and the same thing holds good of the vapour of metallic mercury itself, which has the same volume as the metal cadmium, and probably zinc, and the well-known biatomic radicals CO, SO, CH4, but double the volume of the elements oxygen and sulphur. In the present state of our knowledge the speaker was not aware of any sufficient grounds for deciding which of these two constitutions of the free molecule of a biatomic element or radical is to be considered as normal and which is abnormal. On the one hand, mercury, cadmium, and all known biatomic radicals have a molecule containing one atom, while the molecule of oxygen contains two atoms, and that of sulphur two at high temperatures and six at lower temperatures. Selenium is at high temperatures like sulphur. It has been amply shown by Dr. Odling and others that tin is biatomic and tetratromic in its two chlorides, and its compounds with the organic radicals and chlorine, &c., leave no room for doubt on the point. By similar chains of evidence the remaining metals can be shown to belong to the great biatomic class containing already so many. The vapour densities of the so-called sesquichlorides of iron, aluminium, and chromium, as determined by Deville, -show that the molecule of each of these bodies contains two atoms of metal and six atoms of chlorine, in fact, the same quantity of metal as the molecule of the sesquioxide: this fact has been held to be an anomaly from the point of view adopted regarding their atomic weights. The speaker believed, however, that so far from being anomalous, these vapour densities are the least which can be reconciled with the conclusion that the metals permanently combine with even numbers of atoms from the first family, for if one atom of iron could on occasion combine with three atoms of chlorine to form one molecule, the law respecting it would assume the not very wise formthat iron combines with an even number of atoms from the first family, except when it combines with an uneven number! The fact is that the sesquichlorides are not exceptions to the law, as at first sight they are suspected of being. Precisely the same remarks apply to the so-called subchloride of sulphur of which the molecule S,Cl, as reby the law. So also cyanogen CN2, acetylene C,H2, ethyle, CH, &c., &c. Amongst exceptions, the speaker mentioned nitric oxide and calomel, both of which have vapour densities corresponding to the molecular formulæ NO and HgCl. Many compounds are known to undergo decomposition on evaporation, and to be reproduced on condensation; thus NH2O yields the two molecules NH, and H2O, each with its own volume, as also SO,H, yields SO, and H2O. SO,H2 and PC1, are also known to yield on evaporation vapour corresponding to a breaking-up into two molecules; and there are strong reasons from analogy, as well as experimental evidence, to believe such decomposition. As, however, a high authority seems inclined 53 to doubt the decomposition, the matter may be considered as still sub judice. The existence of basic salts of mercury or copper, when apparently monatomic, is another class of apparent exceptions to the law. For if, in the sub-nitrate of mercury, the atom of metal really replaced one atom of hydrogen, just as potassium does in nitrate of potash, there ought not to be basic sub-nitrate of mercury any more than a basic potash salt; whereas, if the sub-nitrate of mercury contains, as the speaker asserted, in one molecule two atoms of metal and two atoms of the salt radical of the nitrates (NO), then a basic salt is as natural and intelligible a compound as the basic nitrate of the red oxide. The action of ammonia on calomel confirms the molecular weight HgCl2; for the compound NH,Hg,Cl, formed simultaneously with sal ammonia, proves that twice (HgCl) takes place in the reaction. CANTOR LECTURES. "On Chemistry Applied to the Arts." By Dr. F. CRACE CALVERT, F.R.S., F.C.S. LECTURE IV. DELIVERED ON THURSDAY EVENING, APRIL 21, 1864. ANIMAL FATTY MATTERS, the various processes for liberating them from the tissues in which they are contained. Th ir composition and conversion into soap. Composite candles. The refining of lard. Codliver, sperm, and other oils. Spermaceti and wax. Ir will be quite out of the question for me to enter upon a general description of the properties and composition of fatty matters, as to do so would be to undertake far too wide a field of research. All that I can attempt in this lecture is to give an idea of their composition, and to describe some of their most recent applications to arts and manufactures. The question of the source of the fatty matters in herbiverous animals has been the subject of a great number of scientific researches, but those of Baron Liebig, Dumas, Boussingault, Payen, and Milne Edwards have left no doubt that when the food of an animal contains a sufficient amount of fatty matter, this is simply extracted from the food, and stored or consumed according to the animal's habits, that is to say, its consumption is in ratio to the activity of the animal; thus, an animal in a state of great activity is comparatively thin, but when confined in a pen or stall it quickly fattens. These gentlemen also proved that when the food is deficient in fatty matters a portion of the amylaceous or saccharine matter becomes converted into fatty matter. The most decisive experiments on this head were made by Mr. Milne Edwards, who found that when bees were confined under a glass shade, with no food but honey, they converted the greater portion of it into wax. Notwithstanding these proofs, however, chemists found it difficult to understand how substances so rich in oxygen as amylaceous ones become converted into a class of matters containing so little of that element, but Baron Liebig has recently published a paper which has partially solved this problem, showing that animals give off during respiration a larger amount of oxygen than is contained in the air inspired, which excess must be derived from certain organic substances circulating in the blood. Fatty matters may be classed under two heads, viz., vegetable and animal. The first are generally composed of a solid, called margarine, and a liquid, called oleine. The latter generally contains three substances, viz., two solids, stearine and margarine, and one liquid, oleine. I say generally, because there are exceptions; thus, in palm oil palmetine is found, in linseed oil linoleine, in sperm oil spermaceti, and in waxes several peculiar acids. Let us now examine the composition of some of the most abundant fatty matters found in animals. The knowledge of the composition of these substances, of suet for example, was most unsatisfactory until 1811, when my learned and eminent master, M. Chevreul, published his 54 Cantor Lectures. also that oxide of glyceryle, as it is liberated from the Stearic acid, 3 (C6sH6605), Glycerine, C,H,O6-4 HO 66 In fact, the researches of this eminent chemist on the synthesis of organic substances have effected a complete revolution in the last few years in that branch of organic chemistry. I shall now proceed to give you a rapid outline of the properties of these substances. Stearic acid is a white crystalline substance, fusible at 158° F., soluble in alcohol and ether, insoluble in water, and saponified by alkalies. July 30, 1864. substitute for fulminating mercury, by its discoverer, Professor Sobrero. The application in medicine of glycerine has been greatly extended by its highly hygrometric properties. Thus, bandages moistened with glycerine remain constantly moist, because the glycerine attracts moisture from the air as fast as it is lost by evaporation. It has also been found eminently useful in diseases of the eye and ear. Glycerine boils at 527°, but when distilled is partly decomposed into a peculiar oily fluid, of a noxious odour, called acroleine. M. Berthelot has succeeded, by fermentation, in converting glycerine into alcohol. Again, Mr. George Wilson, F.R.S., the talented director of Price's Patent Candle Company, has applied glycerine with great success to the preservation of vegetable and animal substances. Another useful employment of glycerine is its substitution for water in gasometers, where the evaporation of the latter is a source of serious loss. Its addition to a soap solution increases the facility of forming soap bubbles to an extraordinary degree. In fact, by its aid, bubbles of seven or eight inches diameter can be produced, exhibiting most beautiful purple and green colours, the beauty of which is greatly enhanced, as Mr. Ladd will show you, when illuminated by the electric light. To prepare this peculiar soap solution, the following proportions are stated to be employed :-Distilled water, 5 ounces; soap, of a drachm; glycerine, 2 drachms. The extraction of the fatty matters of animals from the tissues enveloping them is a simple operation. The old proin introducing the suet into large iron pans and applying cess of doing this, technically called "rendering," consisted heat, which caused the fatty matters, by their expansion, the contents of the boiler, which were left to stand for a few to burst the cells confining them, and to rise to the top of hours, and the liquid fat was then run off. The organic tissues remaining with a certain amount of fat at the bottom of the boilers were removed and subjected to pressure so as to separate the rest of the fat, the organic tissues remaining behind being sold under the name of scraps for feeding dogs, &c. As this operation gives rise to noxious vapours, causing thereby great annoyance, other methods have been generally adopted. For instance Mr. D'Arcet's, the leading feature of which is to place in a boiler say 350 lbs. of suet with 150 of water and fifteen of sulphuric acid, carrying the whole to the boil for some hours, when the sulphuric acid dissolves the organic matters and liberates the fatty ones, which are then easily separated from the aqueous fluid. Mr. Evrard's process appears preferable. He boils the fatty matters with a weak solution of alkali; or, in other words, he uses 300 lbs. of suet with half a-pound of caustic soda dissolved in twenty gallons of water, carrying the whole to the boil alkali the tissues are swollen and dissolved and the fat by means of a jet of steam. Under the influence of the liberated. By these operations a better quality of fat is obtained and no nuisance is created. It is found advanGlycerine, or the sweet principle of oils, was discovered tageous to purify or bleach the above fatty matters by the in 1779, by Scheele, who extracted it in boiling oil of sweet following means. Mr. Dawson's process consists in passing almonds with oxide of lead, which, combining with the air through the melted tallow, and Mr. Watson's in heatfatty acids, liberated the oxide of glyceryle, and this, in ing melted fatty matter with permanganate of potash. Both combining with water, formed glycerine. In consequence these processes, as you will perceive, are based on the of the numerous applications of glycerine in medicine, the oxidation of the colouring organic matter. Some tallowFrench have manufactured this substance on a large scale melters further clarify their tallow by adding lbs. of from the liquors in which they have saponified their fatty alum in powder to Ico lbs. of melted tallow, which sepamatters into soap; but the purest and most extensive rates and precipitates any colouring matter. The white supply is furnished by Price's Patent Candle Company. snowy appearance of American lard, which is rather deIn the course of this lecture I will give you a description ceptive to the eye than profitable, is obtained by thoroughly of its preparation as carried out at their works. Gly-mixing, by means of machinery, starch in a state of jelly cerine is a colourless, syrupy fluid, of sweet taste, and with a little alum and lime, with the fatty matter, by which sp. gr. 128, highly soluble in water and alcohol, combining means two ends are attained-viz., the introduction of 25 easily with hydrochloric, hydrobromic, benzoic, tartaric, per cent. of useless matter, and a perfect whiteness from &c., acids, forming neutral compounds. Diluted nitric acid the high state of division of the same. converts it into glyceric acid; concentrated nitric acid into from fish are generally obtained by boiling those parts of The fatty matters nitro-glycerine, or a substance exploding with violence by the fish containing them with water, when the fatty matters percussion, which has caused it to be proposed as a rise to the surface of the fluid, and one whale has been Margaric acid is a solid crystalline substance, presenting the same properties as stearic, excepting that its fusing point is 140°. Oleic acid is a fluid remaining in that state even at several degrees below the freezing point of water, and is also soluble in alcohol and ether, but not in water. NEWS together with a small amount of colouring-matter, and of phocenic acid, which gives to whale oil its disagreeable colour and odour. Many attempts have been made to sweeten whale oil by the use of weak caustic lye, milk of lime, sulphuric acid, and steam; but although a great improvement has been effected, the oil is still recognisable by its unpleasant odour. I have no doubt in my mind, from experiments made by my friend, Mr. Clift, that fish oils might be obtained as sweet as vegetable oils, if proper means for their extraction were adopted. Allow me here to revert to animal fats, to show you that their comparative hardness or solidity, as shown by the following table, depends upon their relative proportions of stearine and margarine, or oleine : M. Pelouze proved some years ago that the rancidity of ordinary animal as well as vegetable oils is due to a fermentation; that is to say, that under the influence of the azotised principle associated with all fats, the fatty matters split into their respective fatty acids and glycerine, which in their turn undergo a further change, resulting in the production of volatile fatty acids, such, for example, in the case of butter, as butyric, caproic, capric, and caprolic acids; in the case of goat's milk, hirsic acid; of fish oil, phocenic acid. Further, M. Pelouze demonstrated that in the case of olive oil this change occurred a few hours after the crushing of the berries, the oil thereby coming in contact with the albuminous principles or ferment. I shall now have the pleasure of calling your attention to some of the special applications which fatty matters receive. The first of these arises out of the action of alkalies upon these substances, the result of which is the conversion of an insoluble matter (oil) into a soluble one (soap). I shall not enter into minute details of this well-known manufacture, but content myself with touching upon some of the most recent improvements. The usual mode of making soap is to add animal fats or vegetable oils to a weak lye, or caustic solution, carrying the mixture to the boil by means of steam-pipes passing through the vessel above a false bottom, and keeping the whole in constant agitation by means of machinery. During this operation the oxide of sodium replaces in the fatty matter the oxide of glyceryle, and when the lye is killed, that is to say when all its alkali is removed by the oil, a fresh or stronger lye is added, and these operations are repeated until the manufacturer considers that the matter is nearly saponified, which is easily judged of in practice. He then proceeds with a second series of operations, called salting, which have for their object to separate the glycerine and impurities from the soapy mass, and also to render the latter more firm and compact, in fact, to contract it. This is effected by treating it with stronger lye mixed with a certain quantity of common salt, and allowing it to stand for a few hours, so that the mass of soap may separate from the fluid containing glycerine and other impurities. When the second series of operations are finished the clarifying or finishing process follows: this requires the use of still stronger lye and salt, which not only complete the saponification, but separate any remaining impurities; the semifluid mass of soap is then allowed to stand for twelve hours, when the soap is either run or ladled into large wooden moulds, and allowed to stand until quite cold. After standing for a day or so, the wooden frame is removed from the solid mass of soap, when it is divided into bars by means of a brass wire. The difference between white curd and mottled soap is caused by the addition to the fluid mass of soap of about four ounces of alum and green copperas to every 100 lbs. of soap, which gives rise to an alumina and ferruginous soap, which, on being diffused through the mass by means of agitation, mottles or marbles the mass when cool. When well prepared this is the most economical soap, as no large quantity of water can be introduced to weight it, because this would cause the separation of the mottling material from the soap. Fancy soaps are prepared in the above rials and the addition of various perfumes. Rosin or yellow manner by the employment of a better quality of matesoap, as its name implies, is one in which a portion of the fatty matters is replaced by rosin, which is added to the soap paste when there is but little aqueous solution of alkali left to dissolve it, so that the rosin can at once enter into the composition of the soap, instead of being dissolved in the alkaline lye and lost. Rosin soaps, nearly white, are now manufactured, owing to the discovery of Messrs. Hunt and Pochin, who have succeeded in obtaining nearly white rosins by distilling common rosin with the aid of superheated steam. Silicated soaps are much used in America, owing to their cheapness, which is due to the introduction of a certain amount of silicate of soda. Transparent soap, the method of making which was so lung kept secret, is now known to be obtained by dissolving soap in alcohol and allowing a concentrated solution of it to cool slowly, when it is poured into moulds and allowed to solidify. One of the most useful and recent improvements in soapmaking is that which enables the manufacturer to produce what is called glycerine soap, which is characterised by the retention of the glycerine of the fatty matter. Its manufacture only occupies a few hours, instead of several days, as is the case with ordinary soap. It is prepared by employing 63 parts of fatty matter, 33 of water, and 5 of alkali, which are heated to a temperature of between 350° and 400°, for two or three hours, when the mass is entirely saponified, and then has only to run into moulds to be ready for the market. But the most important discovery connected with the saponification of fatty matters by means of alkali is that recently made by M. Mèges Mouries, for this gentleman has arrived at the remarkable result of saponifying fatty matter in the space of twelve hours, and, what is more extraordinary still, at natural temperatures. If we connect this fact with the one that caustic soda is now manufactured by tons, it appears highly probable that in a few years the fatty matters of Brazil and Monte Video, instead of being sent to this country as such, will be converted into soap there, and imported thence by us in that form. M. Mouries has discovered the fact that fatty matters are susceptible, under peculiar circumstances, of being brought into a globular state, and that when in that state they present new and peculiar properties. Thus, for example, fatty matters, when kept in a damp state, usually become rapidly rancid, whilst when in the globular state they may be kept for a very long period without undergoing that change. This peculiar state can be imparted to fatty matters by melting them at 130° and adding a small quantity of yolk of egg, bile, albuminous substances, or, what is best, a solution of alkali, composed of five to ten parts of alkali for every 100 parts of oil, at the same temperature, agitating the whole for some time to bring the fatty matter into a globular condition. If at this stage the action of the alkali is continued and the temperature is raised to 140°, it is found that instead of the fatty matters requiring a long time to |
