1888.] Prafulla Chandra Kay on Copper- Magnesium Group. 283 
formation of heterogeneous deposits. The conclusions which they 
have drawn from the analysis of such preparations are therefore 
unwarranted. It seems evident that the results of former investi- 
gations, as well as those obtained by me, prove the existence of 
“double-double” sulphates of definite composition. The chemical 
affinity which determines the formation of such compounds is not 
indeed very powerful, but its influence is quite unmistakable if 
proper care be taken to avoid conditions under which it is necessarily 
obscured. Professor Crum Brown pointed out to me that there is 
room for subsequent research in the determination of the limits of 
the composition of the solution between which given definite com- 
pounds separate out. I accordingly made some experiments in this 
direction, but must leave any discussion of this interesting subject 
to a future date. The whole question seems to me worthy of the 
attention of those who can find time to carry out the numerous and 
often troublesome analyses necessary for the solution of the various 
problems which present themselves. 
In conclusion, I beg to offer my grateful thanks to Dr John 
Gibson for his help and advice, and for the many important sugges- 
tions which he has made throughout the course of the investigation. 
I am also deeply indebted to Mr T. F. Barbour for the ready and 
constant aid I have received from him while drawing up this paper ; 
indeed, it is not too much to say that without Mr Barbour’s un- 
grudging labour and sacrifice of time, the table of the Eesults of 
Analyses could not have been presented in the very complete form 
in which it now appears. I also gladly avail myself of this op- 
portunity to express my cordial thanks to Professor Crum Brown 
for counsel, criticism, and encouragement during the progress of 
my work. 
2. On the Chemical Composition of the Water composing 
the Clyde Sea Area. Part II. By Adam Dickie. 
This is merely the concluding portion of the tables attached to 
a paper which was formerly communicated to the Society by Dr 
Murray, and which is printed in your last Part of Proceedings. 
I need only state that the same methods described in that paper 
