95 



It appeared to me undesirable merely to reply to Professor Leh- 

 mann, that I had expressly stated that the indigo and protosulphate 

 of iron tests were used, and gave as decided proof of the presence of 

 nitrous acid in the urine as Price's test gave ; and that sulphurous 

 acid could not have produced the same effect as nitrous acid in these 

 tests. It seemed more desirable to repeat the experiments which 

 had been made in Professor Lehmann's laboratory on the action of 

 sulphurous acid, and on the effect of using phosphoric instead of 

 sulphuric acid in the distillation of the urine. 



I was fortunate enough to obtain the assistance of Mr. Malone to 

 carry on the experiments continuously from day to day, and through 

 the kindness of Dr. Hofmann this was done in the College of Che- 

 mistry. 



1st. On the action of sulphurous acid on starch and iodide of 

 potassium and very dilute hydrochloric acid. 



In England it is by no means well known that sulphurous acid 

 decomposes hydriodic acid. On the contrary, theoretically it should 

 not liberate iodine, and experimentally not only does it not liberate 

 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 



