acids are bibasic. In the following exercises the salts of these sulpho-acids will be introduced, as well as the salts of the bibasic organic and inorganic acids. EXERCISES. 154. Write out the formula of the following salts:Primary carbonate of potassium, secondary sulphite of sodium, primary sulphate of ammonium, secondary oxalate of potassium, tartrate of potassium and sodium, primary sulpho-benzoate of sodium, acid succinate of sodium, neutral malate of zinc, terephthalate of silver, neutral suberate of lead, primary sulphacetate of sodium, benzo-glycolate of ammonium, neutral sebate of lime. 155. There is a basic sulphate of copper having this composition (employing the old atomic numbers), 4 Ču O, SO: formulate it on the water type, employing the new atomic numbers. (4.) BIATOMIC ETHERS. 825. The neutral biatomic ethers are produced in the same way as the monatomic ethers. When the corresponding acid is not volatile, the neutral ether of the acids is not volatile. In this case we cannot employ distillation as a mode of preparing them, but we operate thus;-hydrochloric acid gas is passed into the solution of the organic acid in alcohol; we neutralize the acid liquid with a carbonate, and we repeatedly agitate with ordinary ether: the ether salt is dissolved by the ether, and is left as a residue on the evaporation of the latter. These neutral ethers can contain two different alcohol radicals. They are obtained by the distillation of two vinic salts, thus : 826. In contact with water, but especially with caustic potash, the neutral ethers are decomposed either into alcohol and a vinic salt, or into alcohol and a metallic salt of the corresponding acid. 827. Ammonia transforms the neutral ethers either into an alcohol and a diamide, or into an alcohol and ether of the acid amide, thus: 828. The acid ethers are produced when we heat an alcohol with the bibasic acids. In the free state these acid ethers are generally unstable, and are decomposed promptly by ebullition with water, or with an alkali, into alcohol and the corresponding acid. Generally they are not volatile without decomposition. They form monobasic salts, ordinarily more stable than themselves. These salts can be employed, as we have seen, in double decompositions, for transporting the alcohol radicals into other combinations. They are analogous, as regards composition and acidity, to the primary salts of the bibasic acids; but the acids in these acid ethers do not give their usual reactions with reagents. Thus, in the sulphovinates, the sulphuric acid is not precipitated by salts of baryta in the same manner as it is from metallic sulphates; but a prolonged contact of these ethers with water decomposes them; the sulphuric acid can then be detected. This nonprecipitation of sulphuric acid by baryta is not limited, however, to the acid ethers; in some, at least, of the neutral ethers it is not precipitated. 829. We shall now give a course of exercises, in which the student will have to write out the formulæ of the neutral ethers of the bibasic acids, and also the salts formed by inorganic bases with the acid ethers. EXERCISE. 156. Write out the formulæ for-Primary carbonic ethyl-ether (carbovinic acid), secondary carbonic ethylether (carbonate of ethyl), primary sulphuric amyl-ether (sulphamylic acid), carbovinate of potassium, secondary sulphuric methyl-ether, sulpho-methylate of calcium, oxalovinic acid, tartro-methylate of barium, sebate of ethyl, suberate of methyl, pimelate of amyl, fumarate of ethyl, malovinate of barium, succinate of methyl. TREBLE MOLECULE. H1 H1 POSITIVE Group. 830. This group embraces-(1) The metallic derivatives of water. (2) The triatomic alcohols. (1.) HYDRATES OF THE METALS PROPER (PRIMARY DERIANHYDROUS OXIDES (SECONDARY DERI VATIVES). 831. Primary derivatives. The sesqui-atomic and triatomic metals, given under the treble molecule of hydrogen (H, H,), form hydrates on the type of a treble molecule of water; the general formula of these hydrates is, therefore, MO, and MO.. M" 832. Secondary derivatives.-The general formula of the anhydrous oxides of the sesqui and tri-atomic metals is M," M2" O, and M" 833. The sulphides, &c., of these metals are, of course, constructed on the same type, the sulphur, &c., taking the place of the oxygen. (2.) TERATOMIC ALCOHOLS. (General formula, C2H;-10.) 834. Glycerine is the only alcohol belonging to this class which has yet been discovered. As it can be prepared artificially, and the manner in which it is formed is well understood, there can be no doubt that other members of the group will be formed, and it is not unlikely that some may be found to exist either in the vegetable or animal kingdom. The formula of glycerine is CHO,. 835. Properties.-In its pure state glycerine forms a nearly colourless and very viscid liquid, of specific gravity 1.27, which cannot be made to crystallize; it has an intensely sweet taste, and mixes with water in all proportions; its solution does not undergo the alcoholic fermentation, but when mixed with yeast and kept in a warm place, it is gradually converted into propionic acid. It has no action upon vegetable colours. Exposed to heat, it volatilizes in part, darkens, and becomes destroyed, acrolein being one of its' products of destruction. 836. Glycerine was discovered by Scheele in 1779; he named it "sweet principle of oils," from its sweet taste. The fixed oils and fats are compound ethers; the acids in these ethers belong to the first or second series of the monobasic organic acids; the ether which exists in all oils and fats hitherto examined, with the exception of spermaceti and the different varieties of wax, is the ether of glycerine. Saponification of oils and fats is nothing more than the decomposition, by means of an inorganic base, of these compound ethers; the inorganic base combines with the acids, glycerine being set free. To obtain glycerine by saponification, the inorganic base best adapted for the purpose is oxide of lead, because, by forming with the acids insoluble salts, it separates them completely from the glycerine; and the slight excess of oxide of lead which dissolves in the aqueous solution of the glycerine is easily removed, as sulphide, by adding a little sulphuretted hydrogen. But as glycerine has now become an article of commerce, the scientific chemist has no need to prepare it; it is prepared commercially by separating the acids and the glycerine by superheated steam. 837. Pasteur has shown that glycerine is always formed during the alcoholic fermentation of sugar, to the amount of about 3 per cent. of the sugar decomposed, and that it occurs in all fermented liquors, especially wine. 838. Preparation.-Glycerine can be prepared artificially either from terbromide of allyl, or terbromhydrine (C, H," Brs), by treating either of these bodies with acetate of silver, bromide of silver and triacetine being formed; glycerine is obtained from triacetine by decomposing this latter substance with baryta water; the liquid is freed from excess of baryta by means of carbonic acid, and evaporated; the residue is treated with anhydrous alcohol, containing a little ether, and the solution thus produced is evaporated. The glycerine then remains in the form of a syrupy liquid, very soluble in alcohol and water, but insoluble in ether. 839. Bromide of bromopropylene, C, H, Br" Br2, which is isomeric with terbromide of allyl and terbromhydrine, yields but a very small quantity of triacetine when treated with acetate of silver. 840. Chemical properties. We must keep constantly in mind, in considering the chemical changes which this triatomic alcohol undergoes with many reagents, that it is constructed on the type of three atoms of water, that three out of the six atoms of hydrogen in three atoms of water remain in the alcohol, and that they are capable of being replaced by simple and compound radicals; three series of bodies can, on this account, be obtained from this triatomic alcohol, whilst only two series can be obtained from the biatomic, and one series from the monatomic alcohols. 841. Substitution of the halogens for the typical hydrogen. If glycerine is saturated with hydrochloric acid gas, and the solution is maintained for several hours at 212° F., and if it is neutralized subsequently with carbonate of soda, and agitated with ether, the ether dissolves out an oil-like body, which is left on evaporating the ether; this body has an etherial odour and a sweet taste. It is miscible with water and ether. Its density is 131, and it boils at 441° F. It is called monochlorhydrine, and its empirical formula is C, H, CIO,; its rational formula is (C, H1)") evidently H2 } O,. It has already been remarked that three series of bodies could be obtained from glycerine from its containing three replaceable atoms of hydrogen. Monochlorhydrine is a member of the first series of compounds; it is the first stage in the conversion of this alcohol into its normal (ter) chloride, the first stage in the conversion of a body constructed on the type of three atoms of water into a body constructed on the type of three atoms of hydrochloric acid. In the substitution of the atom of chlorine for the atom of hydrogen, one atom of oxygen is removed along with the hydrogen; so that it is the substitution of one atom of chlorine for an atom of peroxide of hydrogen, or the residue of water. The following equation expresses the reaction : : |