SODIl'M < IILOKIDE EERTHOLLETS LAWS 



and others). These compounds with hydrochloric acid are generally 

 more soluble in water than the metallic chlorides themselves, so that 

 whilst hydrochloric acid decreases the solubility of MCl m , correspond- 

 ing with energetic bases (for instance, sodium or barium chlorides), it 

 increases the solubility of the metallic chlorides corresponding with 

 feeble bases (cadmium chloride, ferric chloride, tfec.). Silver chloride, 

 which is insoluble in water, is soluble in hydrochloric acid. Hydro- 

 chloric acid also combines with certain unsaturated hydrocarbons (for 

 instance with turpentine, C 10 H 16 2HC1) and their derivatives. Sal- 

 ammoniac, >r ammonia hydrochloride, NH 4 C1 = NH 3 ,HC1, also belongs 

 to this class of compounds. 43 If dry hydrogen chloride be mixed 

 with dry ammonia, a solid compound formed from equal volumes of 

 each is immediately formed. The same compound is formed on mixing 

 solutions of the two gases. It is also produced by the action of 

 hydrochloric acid on ammonium carbonate. Sal-ammoniac is usually 

 prepared by the last method in practice. 44 The specific gravity of sal- 

 ammoniac is 1-55. We have already seen (p. 253) that sal-ammoniac, 



4r> When an unsaturated hydrocarbon, or, in general, an unsaturated compound, 

 assimilates to itself the molecules CL, HC1, SO 5 , HoSO 4 , &c., the cause of the reaction 

 is most simple. As nitrogen, besides the type NX 3 to which NH 3 belongs, forms com- 

 pounds of the form NX 5 for example, NO 2 (OH) therefore the formation of the salts of 

 ummonium should be understood in this sense. NH- gives NH 4 C1 because NX 5 is 

 capable of giving NX 5 . But as saturated compounds for instance, HC1, H 2 O, NaCl, 

 Arc. are also capable of combination even between themselves, therefore it is impossible 

 ; ( deny the capacity of HC1 also for combination. SO 3 combines with HoO, and also with 

 HC1 and the unsaturated hydrocarbons. It is impossible to see the limit here, which it 

 \vas lately wished to establish, by distinguishing atomic from molecular compounds, and 

 regarding, for instance, PC1 5 as an atomic compound and PC1 5 as a molecular one, only 

 because it easily splits up into molecules PC1 5 and Clo. 



44 Sal-ammoniac is prepared from ammonium carbonate, obtained in the dry distilla- 

 tion of nitrogenous substances (Chapter VI.), by saturating the resultant solution with 

 hydrochloric acid. A solution of sal-ammoniac is thus produced, it is evaporated, and 

 in the residue a mass is obtained containing a mixture of various other, especially tarry, 

 products of dry distillation. The sal-ammoniac is generally purified by t sublimation. 

 For this purpose iron vessels covered with semispherical metallic covers are employed, 

 or else simply clay crucibles covered by other crucibles. The upper portion, or helmet, 

 of the apparatus of this kind will have a lower temperature than the lower portion, which 

 is under the direct action of the flame. The sal-ammoniac volatilises when heated, and 

 settles on the cooler portion of the apparatus. It is thus purified from many impurities, 

 and is obtained as a crystalline crust, generally several centimetres thick, in which form 

 it is generally sold. 



In order to demonstrate the very instructive formation of solid sal-ammoniac from 

 the gases NH 3 + HC1 we may proceed as follows : A thin glass tube is filled with ammonia 

 and closed with a cork, and placed in a thick glass cylinder into which a rapid stream of 

 hydrogen chloride is introduced and is then closed with a cork; the inside tube is then 

 broken by violently shaking the apparatus. The ammonium chloride is obtained in white 

 Hakes. A glass rod, or paper moistened with hydrochloric acid, also gives a distinct 

 dond of sal-ammoniac when held over the mouth of a bottle containing a strong solution 

 of ammonia. 



o o 2 



