476 P. C. Ray — Mercurous Nitrite and its Derivatives. [No. 4, 



has tank instead of river water as an alternative to the filtered supply, 

 on the other hand, has a spleen-rate of 14*8, which is almost the same 

 figure as that of Maniktolla, with a similar water-supply. Further, 

 those Wards which are situated immediately on the river bank, but 

 do not possess a filtered water-supply, and consequently get their supply 

 mainly from the river, and to a less extent from tanks, have a rate 

 intermediate between those with filtered water and the inland ones which 

 are dependant entirely on tank water. In short, all the Ward variations 

 in the spleen-rate of the whole area can be explained on the ground of 

 their varying water-supplies in a manner which no other explanation 

 will approach in completeness, so that it is impossible to come to any 

 other conclusion than that the above is the true explanation of the facts 

 recorded. Whether the Anopheles mosquitos play a part by taking the 

 malarial parasite back to the tanks from their human hosts or not must 

 be left to be determined by future experiments, but that a good water- 

 supply is an important prophylactic measure in the lessening the pre- 

 valence of malaria must I think be admitted, and can be safely acted on. 



XVIII. — /. Further Mesearehes on Mercurous Nitrite and its Derivatives. 



II. On Mercurous Iodide and a new Method of its Preparation. — By 



P. 0. Kay, D.Sc. 



[Received 16th July ; Read 1st August, 1900.] 



CONTENTS. 



I. Further Researches on Mercurous Nitrite and its Derivatives. 

 (J ) Preparation of Mercurous Nitrite on a large scale. 



(2) Preparation of chemically pure Mercurous Nitrite, 



(3) Interaction of Mercurous Nitrite and Ethyl Iodide. 



(4) Interaction of Mercurous and Mercuric Nitrites with the 



Nitrites of Silver and Sodium respectively. 

 II. Mercurous Iodide: a new Method of its Preparation. 



(i) 



Preparation oir Mercurous Nitrite on a large scale. 



As the investigations I am about to describe involve the use of 

 comparatively large quantities of mercurous nitrite at a time I shall 



