218 Royal Society, 



iodine, but it hinders the liberation of iodine und stops the formation 

 of the blue colour when Price's test is used and nitrous acid is pre- 

 sent ; and if sulphurous acid be added after the blue colour is formed 

 it makes it disappear. 



Pure sulphurous acid was prepared, some nitre was fused, and a 

 dilute solution was made, and it was tested by Price's test (starch, 

 iodide of potassium and very dilute hydrochloric acid), then the di- 

 lute nitre solution immediately gave the deep blue iodide of starch ; 

 but when much or little sulphurous acid was added previously to the 

 nitre solution, no blue colour at all was produced ; and when, 

 instead of the nitre solution, much or little sulphurous acid alone 

 was added, contrary to the statement of Lehmann, no decomposition 

 of the hydriodic acid could be obtained. 



If instead of pure iodide of potassium it was mixed with iodate of 

 potassa, an immediate blue colour was of course observed. I can 

 only suppose that in this way Professor Lehmann obtained the re- 

 action which he has attributed wrongly to the action of sulphurous 

 acid on hydriodic acid, unless indeed no sulphurous acid at all was 

 present and the acidity of the distillate was unneutralized. Dr. Leh- 

 mann is however right as well as wrong, in saying that Price's test 

 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. 



