Acids. 167 



smoke: in this process the acid in question is 

 formed out of the animal matter employed (which 

 is not confined to this material, blood), and im- 

 mediately seizes the alkali. We have then a prus- 

 siate of potass, which being dissolved in water, 

 and mixed with sulphat of iron (green vitriol), 

 a double decomposition ensues, hydrocyanat of 

 iron falls down in a precipitate, and the alkali is at- 

 tached to the sulphuric acid, forming sulphat of 

 potass, which may be washed off from the colour. 



Phosphoric acid is the direct product of the 

 combustion or oxygenation of phosphorus, 

 which consequently affords more than its own 

 weight of it. This acid, deprived of all its water 

 by heat, is solid, colourless, and of a glassy ap- 

 pearance. It has a very sour taste, without any 

 smell ; is not corrosive to the skin, and readilv 

 deliquesces. 



It dissolves in water, giving out much heat, 

 like the sulphuric. 



It forms with lime an insoluble compound, 

 phosphat of lime, which has the appearance and 

 properties of earths, and is the solid part or base 

 of animal bones, in which it is united to gela- 

 tine, or, in plain language, glue. Hence calcined 

 bones, by proper treatment, yield phosphorus, 

 the oxygen being abstracted by the charcoal em- 

 ployed in the distillation, which is conducted in 

 a sttong heat. It also enters into the composi- 

 tion of many mineral substances, whole rocks 

 being sometimes formed of this substance. 



