LESSONS IN CHEMISTRY. 



m 



Lead Acetate (Pb2C,H,O t + 3H,O), from its aweetiah taate, 



ia called .<< M; / lead; it may bo procured by dissolving litharge 

 in acotio u 



[a a trilmsic plumbic acetate, which in solution 

 fonn ', tin- in.t.-.l i yo-wator. 



Carbonic acid is capable of displacing acetic acid in this salt, 



.vln.-li fact is taken advantago f in tin- production of white lead. 



. .-ll-known aootato ia verdigrit, which is a dibasic 



acetate of coppor (Cu2C,H,O 3 ,CuO,6H t O). " Emerald green," 



i |.ivni.-:.t in \---y frequent UHO, ia an aooto-araonite of copper 



ir,p,,AiO^. 



Butyric And was originally derived from butter, hence ita 

 name. It is bost pn -pared by allowing a mixture of calcic 

 lactato, watur, and old cheese to ferment. The lactic acid ia 

 entirely destroyed, and butyric formed in ita place. 



Valerianic Arid is extracted from valerian root. It is often 

 present in decaying choose, and is readily obtained by oxidising 

 amylio alcohol. 



/'//. .(, ;',/ is the main component of " compo- 

 sition " caiulles. It ia a solid, procured from palm-oil. Super- 

 heated steam decomposes palm-oil into glycerine and free acids. 

 These products are condensed, and subjected to hydraulic pres- 

 sure, which separates the liquid from the solid acids. 



Margnric Acid ia found combined with glycerine in olive oil, 

 butter, human fat, goose fat, etc. Its melting point is 53. 



Stearic Acid, combined with glycerine, is found in almost all 

 fats, but chiedy in mutton suet. If this body be heated in 

 about ten times its volume of ether, upon cooling, oleine and 

 margarine are held in solution, and stcarine crystallises out in 

 pearly scales. 



Soap. If oily matters of which we have enumerated the 

 most prominent constituents bo mixed with water, they will 

 rise to the surface ; but if the water contain an alkali, the 

 oily matter will go into solution, forming an emulsion. When 

 this solution is boiled for some hours, it becomes clear, being 

 a solution of soap. By adding common salt, a curdling is 

 produced. The curds rise to the surface, which, when col- 

 lected and pressed, form soap. The glycerine remaining 

 in the clear liquid soda is the alkali used in hard soaps and 

 potash in soft soaps. Curd soap is made from tallow ; common 

 yellow soap from tallow and palm-oil ; a quantity of rosin being 

 added, which combines with the alkali, since it possesses acid 

 properties. Mottled soap is set to cool in cast-iron moulds, and 

 the mottling is due to the separation of an iron soap that is, a 

 body in which iron oxide is the base combined with the fatty 

 acid. Soaps formed with the alkalies are soluble in water ; not 

 so those formed with the alkaline earths. It is owing to this 

 fact that soap curdles in hard water. Such waters generally 

 contain calcium and magnesium salts, and when soap is dis- 

 solved in them, a double decomposition occurs. The alkali of 

 the soap joins with the acid combined with the calcium, while 

 the calcium unites with the acid of the soap, thus forming a soap 

 which is insoluble, and which, therefore, appears as curds. 



Lead-plaster is a soap which has the oxide of lead for its base. 



Candle-making. It has already been said that, under the 

 influence of super-heated steam, glycerine will separate from the 

 fatty acids ; but two other methods are in use. Milk of lime 

 is added to the melted tallow, and thus an insoluble soap is pro- 

 duced, leaving the glycerine in the solution, which is drained off. 

 By cautiously adding sulphuric acid, the lime is separated as 

 sulphate, and the fatty acids rise to the surface. They are 

 decanted off, washed, and cast into thin plates, which are sub- 

 mitted to hydraulic pressure, by which the oleio acid is forced 

 out, and the white residue is ready for casting in the candle- 

 moulds. In the third method, which is much used in this 

 country, the separation of the fatty acids is effected by sulphuric 

 acid at a high temperature, 177. The acids are of a dark 

 colour, and are therefore distilled by steam passed through 

 pipes heated nearly to redness. The distillation begins a little 

 above 200. The fat is then submitted to pressure, and is fit 

 for the moulds. 



Glycerine (C S H 8 O S ). We have seen how this substance may 

 be separated from fats. It is a clear viscid liquid, of a sweet 

 taste. Like sugar, it possesses antiseptic properties, and 

 pleasantly affects dry or chapped skin. It is a triatomic alcohol, 

 its radical glycerile (C,H 5 ) being triatomic. Like the other 

 alcohols, it forms many series of derivatives. 



Nitro-glycerine (C 3 H S 2N0 2 ,O S ) is being used for blasting with 



great effect. It ia made by allowing glycerine to fall, drop by 

 drop, into a cooled mixture of equal meMnrea of nitric sad sul- 

 phuric acida, an in the making of gun-ootton. It* ezploaire 

 force ia very great. 



Subjoined ia a complete lint of the monobaaic acida, which 

 are framed upon the general formula C'nH^O,, and the promi- 

 nent member* of which have juat been described : 

 Formic . . CH.O, Caprio . . C.H,.O, Steario . . C..H..O, 

 Acetic . . C.H.O, Pelargonlo. C,H,.O, Aracbio. . C,.H. O, 

 Propionio .C.H.O, Hutic . . . C,.H, O, Bebenie . . C..H..O, 

 Butyric . .C.H.O, Laurie . . C,,H,.O, Hyamio . . C..H..O, 

 Valerianio . C.H..O, Myriatlo .C,.H,,O t Crotto . . C,,H,.O, 

 Caproic . . C,H,,O, Palmitic . C,.H,,O, Helia 

 (Enanthylic. C,H,.O, Margario . C 1T H,.O, j 



Of the diatomic acida, the moat worthy of notice 



Lactic Acid (H,C 3 H S O,). This acid ia produced from the 

 sugar of milk by a peculiar change called the lactic fermenta- 

 tion. When thin has taken place, the milk ia said to have 

 " turned." It becomes thick by a deposition of caaeine. It ia 

 found in many animal juices. It forms with baaea lactatea. 



Oxalic Acid (C,O S ) is found in combination with soda or 

 potash in many plants, as sorrels, lichens, etc. It ia prepared on 

 a large scale by heating sawdust with a mixture of sodic and 

 potassic hydrate. The oxalatos thus formed are dissolved oat 

 by water. To this solution milk of lime is added, and the inso- 

 luble calcium oxalate falls. The acid is freed by means of diluto 

 sulphuric acid. 



Malic Acid (C 4 H,O S ) is the cause of the acidity in moat un- 

 ripe fruits. Ita name is derived from rnalum, an apple. Mixed 

 with oxalic and phosphoric acids, it is found in rhubarb, and 

 is also present in combination with lime in tobacco leaves. The 

 acid is generally procured from the berries of the mountain-ash. 

 The fact that malic acid does not give a precipitate with lime- 

 water, is a means of distinguishing it from oxalic, tartaric, 

 raccinic, and citric acids. 



Tartaric Acid (C 4 H a O e ) is procured from the crust which the 

 Continental wines deposit, which is mainly composed of hydro- 

 potassic tartrate. When boiled with chalk, a precipitate of calcic 

 tartrato is obtained (C 4 H 4 CaO B ). This salt is decomposed by 

 sulphuric acid. The solution of free tartaric acid thus procured 

 is evaporated in vacuum pans, and the acid crystallises out. 



Tartaric acid and its derivatives are invested with much 

 interest on account of the action they possess on polarised 

 light, for which a larger work must be consulted. 



It is used to make effervescing draughts, seidlitz powders, 

 etc. ; also it is much employed by the calico-printer to remove 

 the mordants from certain parts of the fabric. 



Cream of Tartar is the argol or crude tartar taken from th't 

 inside of the wine casks. It is purified by crystallisation. 



Tartar-emetic [2(KSbO,C 1 H 4 O a ),H,0] is procured by boflin-? 

 pure antimonic oxide with hydropotassic tartrate. It acts as a 

 violent emetic. Sulphuretted hydrogen discovers its presence 

 by throwing down the orange-coloured antimonious sulphide. 



Citric Acid (C a H g O,) is the acid of lemons. It is employed 

 in medicine as an anti-scorbutic, and is used by the dyer. 



Tannic Arid (C^H M O }1 ). There is an astringent principle 

 widely diffused through the vegetable kingdom. It is found in 

 the bark and leaves of most forest trees. This principle ia 

 generally some modification of tannin. It gives with ferric salt- 

 a dark precipitate ; black in the case of gallic acid ; dark-green 

 with catechu and kino ; and grey with rhatany. The gall-nut 

 contains as much as two-thirds its weight of tannic acid, from 

 which it is usually extracted. We have seen its use in the 

 manufacture of leather. To make ink, the following is a good 

 recipe : Digest Jib. of bruised gall nuts in a gallon of cold 

 water, add 6oz. of ferrous sulphate, with an equal weight of 

 gum-arabic, and 4 or 5 drops of kreasote, to prevent the ink from 

 becoming mouldy. Let this digest at the ordinary temperature 

 for two or three weeks, then decant (Miller). 



Gallic Acid is obtained from tannin by the action of sulphuric 

 or hydrochloric acid, which causes water to be assimilated. 



thus: 



Tannin. Gallic Acid. QlaooM. 



C,,H,,O IT + 4H a O =s 3C,H.O. + C.^.O.. 



Pyrogallic Acid is got from gallic by sublimation. It is much 

 used in photography for intensifying the film of negatives. 



There are many acids of less note than those alluded to, but 

 they do not require attention in an elementary work. 



