48 FIRST PRINCIPLES. 



As alkalies have the property of dissolving resins, waxes, and 

 fat, all of which are chemically allied to each other ; ammonia in 

 the air will spoil the varnish of a carriage, and will tend to 

 remove fat and bees'-wax from leather, and will consequently 

 make it dry and liable to crack. Coachbuilders remove the 

 varnish from carriages in the same way by using a solution of 

 ammonia, caustic soda, or caustic potash. 



To take the case of the removal by ammonia of bees'-wax 

 (which consists mostly of myricyl palmitate), or of a varnish 

 containing bees'-wax, we have the following equation : 



C 30 H 61 C 16 H 31 2 + NH 4 HO = NH 4 C 16 H 31 O 2 + C 30 H 6l OH. 

 Myricyl palmitate. Ammonium Ammonium Myricyl 



hydrate. palmitate. alcohol 



(a soluble soap). (soluble). 



With the exception of the watery vapour, the products of 

 the decomposition of urine and dung do not appear to have 

 any injurious effect on steel. Besides the removal of fatty 

 matters, ammonia has seemingly no destructive action on 

 leather, which, however, falls a ready prey to bacteria, in 

 the event of their reaching it, by, for instance, its becoming 

 soiled with decomposing dung or urine. 



In the manufacture of leather, the skins are placed for 

 a brief period in "dung bate," which is a mixture of 

 dung and water, and which, owing to the action of bacteria, 

 will destroy the skins if they are left too long in it. This 

 action of bacteria, and the property ammonia has of re- 

 moving fat and darkening leather, account for the fact that 

 keeping saddlery and harness exposed to the emanations of 

 a stable has a bad effect on them. 



SOAP. 



Ordinary soap is formed by the chemical union of certain 

 fatty substances with soda or potash. In tallow, which is used 

 to make common hard soap, the fatty substances consist of 



