1824.] On some of the Aeriform Compounds of Nitrogen. 299 



reason express surprise at its having so far escaped notice,* 

 were I not aware how many facts commonly remain disregarded, 

 merely for want of explanation. It is evident that I once, and 

 for a long time, overlooked the inference that is to be drawn 

 from this affection ; and if the disorder had not happened to 

 me a second time, I might never have reconsidered its cause. 



Even since the preceding pages were written, I have met 

 with two more cases of this disease. One of my friends has 

 been habitually subject to it for 16 or 17 years, whenever his 

 stomach is in any considerable degree deranged. In him the 

 blindness has been invariably to his right of the centre of vision, 

 and, from want of due consideration, had been considered as 

 temporary insensibility of the right eye; but he is now satisfied 

 that this is not really the case, but that both eyes have been 

 similarly affected with half- blindness. This symptom of his in- 

 digestion usually lasts about a quarter of an hour or twenty 

 minutes, and then subsides, without leaving any permanent im- 

 perfection of sight. 



I have not seen the subject of the 5th case, but I am informed 

 that he has had many returns of this affection, generally at- 

 tended with head-ach, and always lasting about 20 minutes, 

 with very little variation. 



Article XVI. 



Experiments on the Analysis of some of the Aeriform Compounds 

 of Nitrogen. By William Henry, MD. FRS. &c. &c.f 

 (Communicated by the Author.) 



1. The Analysis of Nitrous Oxide and Nitrous Gas. 



The methods of analyzing nitrous oxide and nitrous gas, de- 

 scribed in the following pages, derive any value they may 

 possess, from their enabling us to demonstrate the composition 

 of those gases, by processes which admit of being more 

 quickly executed than the methods already in use, and which, 

 at the" same time, are capable of affording results approaching 

 as nearly to perfect accuracy, as is consistent with the nature 

 of such investigations. The decomposition of nitrous oxide 

 may, indeed, be readily and expeditiously effected, in conse- 

 quence of its forming a combustible mixture with hydrogen gas, 



* Richter, in the third volume of his Elements of Surgery, has a chapter on half, 

 blindness, and part of it relates to what he terms amaurosis dimidiata. From one 

 instance there given, he seems to have seen some cases similar to those I have 

 described; but he has not noticed the corresponding affection of the two eyes, or consi- 

 dered the sympathy between them (Anfangs-gr'unde Der Wundartzeneykunst,vol.iii. 



chap. 16, p. 478.) 



f From Vol. IV, New Series, of Memoirs of the Literary and Philosophical So- 

 ciety of Manchester. 



