PYROZOIC ACID. 17 



then distilled in a retort, and when it begins to get thick, new 

 portions of water are added, and the distillation is continued 

 till no more volatile oil passes into the receiver along with the 

 vapour of water. It is this volatile oil which constitutes the py- 

 rozoic acid. 



It is a limpid liquid of a pale yellow colour, and has a sharp 

 and empyreumatic smell. According to Unverdorben, it is to 

 the presence of this acid that the empyreumatic oils owe their 

 peculiar odour. Its vapours redden litmus paper. It is insolu- 

 ble in water ; but very soluble in alcohol, ether, and the volatile 

 oils. In the dilute acids it does not dissolve. It ought to be 

 kept in well stopped phials, which should be filled with it, because 

 when in contact with the air, it is speedily decomposed, becom- 

 ing brown, and then black and thick. 



It is a very feeble acid, being incapable of decomposing the al- 

 kaline carbonates, even when assisted by heat. Its salts crystallize 

 with difficulty. When exposed to the air, they gradually un- 

 dergo decomposition, a resin being deposited, and, if we believe 

 Unverdorben, a butyrate of the base remains. 



Pyrozoate of potash is formed by dissolving the acid to satu- 

 ration in caustic potash ley. If, during the evaporation, we add 

 an excess of acid, we obtain at first a syrup, then minute crystals, 

 and finally, a dry white mass, split in all directions. This mass 

 bears a strong heat, without decomposition ; but it becomes at 

 last black, and then, according to Unverdorben, water extracts 

 from it butyrate of potash. 



Pyrozoate of lime is soluble in fifteen times its weight of water. 

 When the solution is evaporated, the salt separates partly as a 

 pellicle and partly as a powder. 



Pyrozoate of copper may be formed by double decomposition. 

 It is a light green powder. It is slightly soluble in water, com- 

 municating to that liquid a green tint. It is more soluble in al- 

 cohol, ether, and the fixed and volatile oils. The alkalies partly 

 decompose it, leaving a brown-coloured subsalt. When distilled 

 per se it gives off about half the acid, which it contains, unalter- 

 ed. It gives off also oderin, a little butyric acid, and a brownish- 

 coloured- substance soluble in potash. 



Pyrozoic acid combines also vtifafuscin, forming a brown in- 

 soluble compound, from which potash extracts the acid, leaving 

 the fuscin. 



