96 



for nitric acid fails when sulphurous acid is present. The test fails, 

 not, as he says, because sulphurous acid has the same action as ni- 

 trous acid in liberating iodine, but because it has exactly the oppo- 

 site property of hindering the iodide from being set free even when 

 nitrous acid in small quantity is present. 



It is possible that in distilling the urine with sulphuric acid, the 

 distillation, if carried too far, may give rise to sulphurous acid, and 

 that thus Price's test may fail to detect nitrous acid in the urine. 

 Moreover, portions of the distillate may be projected against the 

 sides of the hot retort, by which the sulphuric acid acting on the 

 organic matter may be decomposed, and minute quantities of sul- 

 phurous acid may be liberated. This sulphurous acid, instead of de- 

 composing hydriodic acid, causes the reformation of hydriodic acid 

 when nitrous acid liberates iodine in Price's test. 



2ndly. Lehmann states that experiments were made by distilling 

 urine to which a few drops of nitric acid were added with phosphoric 

 acid, and that then the distillate gave no reaction with Price's test. 



The following experiments were made with every precaution. 



Anhydrous phosphoric acid was prepared, and it was found to be 

 free from nitrous acid. Some healthy urine was taken and some 

 pure nitrate of potassa, in the proportion of two grains of salt to 

 an ounce of fluid, and distilled with phosphoric acid (ten ounces of 

 urine, twenty grains of nitre, and one ounce of anhydrous phosphoric 

 acid). On concentrating, the neutralized dilute nitrous acid was 

 detected by all the tests, namely, the indigo test, the protosulphate 

 of iron and Price's test. 



In a second experiment, five ounces of urine with five grains of 

 nitre and half an ounce of anhydrous phosphoric acid, gave nitrous 

 acid by all the tests. The distillation was continued until the con- 

 tents of the retort were viscid. 



In a third experiment, three ounces of urine with a grain and a half 

 of nitre were distilled with three drachms of glacial phosphoric acid ; 

 the distillate neutralized and evaporated gave no trace of nitrous 

 acid ; the same urine with the same quantity of nitre and three 

 drachms of sulphuric acid, when distilled, gave a distillate, which 

 when neutralized and evaporated gave decided evidence of nitrous 

 acid. 



In my former paper I showed that by distilling with sulphuric 



