80MUM 581 



and evolve a smell of ammonia, owing to the caustic soda changing 

 the gelatinous organic substance of the bones (which contains carbon, 

 hydrogen, nitrogen, oxygen, and sulphur, like albumin), dissolving it 

 and in part destroying it, whence ammonia is disengaged. Fats, tallow, 

 and oils become saponified by a solution of caustic soda that is to 

 say, they form with it soaps soluble in water, or sodium salts of the 

 organic acids contained in the fats. 35 The most characteristic reactions 

 of sodium hydroxide are determined by the fact that it saturates all 

 acid8 y forming salts with them, which are almost all soluble in water, and 

 in this respect caustic soda is as characteristic 'amongst the bases as 

 nitric acid is among the acids. It is impossible to detect sodium by 

 means of the formation of precipitates of insoluble sodium salts, as may 

 be done with other metals, many of whose salts are but slightly soluble. 

 The powerful alkaline properties of caustic soda determine its capacity 

 for combining with even the feeblest acids, its property of disengaging 

 ammonia from ammonium salts, its faculty of forming precipitates from 

 solutions of salts whose bases are insoluble in water, <kc. If a solution 

 of the salt of almost any metal be mixed with caustic soda, then a 

 soluble sodium salt will be formed, and an insoluble hydroxide of the 

 metal will be separated for instance, copper nitrate yields copper* 

 hydroxide, Cu(N0 3 ) 2 + 2NaHO = Cu(HO) 2 + 2NaNO 3 . Even many 

 basic oxides precipitated by caustic soda are capable of combining with 

 it and forming soluble compounds, and therefore caustic soda in the 

 presence of salts of such metals first forms a precipitate of hydroxide, 

 and then, employed in excess, dissolves this precipitate. This pheno- 

 menon occurs, for example, when caustic soda is added to the salts of 

 aluminium. This shows the property of such an alkali as caustic soda 

 of combining not only with acids, but also with feeble basic oxides. For 

 this reason caustic soda acts on most elements which are capable of form- 

 ing acids or oxides similar to them ; thus the metal aluminium gives 

 hydrogen with caustic soda in consequence of the formation of alumina, 

 which combines with the caustic soda that is, in this case, the caustic 

 alkali acts on the metal just as sulphuric acid does on Fe or Zn. If 

 caustic soda acts in this manner on a metalloid capable of combining 

 with the hydrogen evolved (aluminium does not give a compound with 

 hydrogen), then it forms such a hydrogen compound. Thus, for instance, 

 phosphorus acts in this way On caustic soda, yielding hydrogen phos- 

 phide. When the hydrogen compound disengaged is capable of combin- 



The bones are mixed with ashes, lime, and water ; it is true that m this case more 

 potassium hydroxide than sodium hydroxide is formed, bat their action IB almost 

 identical. 



As explained in Note S, 



