1888.] Prafulla Chandra Ray on Copper- Magnesium Groups. 267 
Monday, 2nd April 1888. 
The Rev. Pkofessor FLINT, D.D., Vice-President, in the 
Chair. 
The following Communications were read : — 
1. Analysis of the “Challenger” Meteorological Obser- 
vations. By Dr Buchan. 
2. On the Conjugated Sulphates of the Copper-Magnesium 
Group. By Prafulla Chandra Ray, Esq. 
Historical and Introductory. 
From time to time memoirs have appeared by various chemists, 
pointing out that there is a tendency among the sulphates of the 
magnesium group to combine with one another in definite molecular 
proportions. This tendency has been brought into connection with 
the fact that these sulphates have almost identical atomic volumes. 
So early as the year 1840 Kopp drew attention to the fact that 
all the vitriolic sulphates have almost the same “ atomic ” volume 
{Ueher Atomvolum, Isomorpliismus und speeifiselien Gewiclit, Ann. 
xxxvi. p. 1, 1840). 
Playfair and Joule {flhem. Soc. Jour., 121, 1848), Schiff, and, 
recently, Thorpe have confirmed and extended Kopp’s classical work. 
Schauffele found (“ Ueber die mehrbasischen schwefelsauren 
Salze der Magnesiareihe,” Jour, fur PraTct. Chem., Iv. 371, 1852) 
that when one sulphate of the magnesium group is dissolved to the 
point of saturation in a previously saturated solution of another, 
the crystals which are obtained contain the component sulphates in 
definite proportions. 
In 1854 Eammelsberg published an elaborate paper on this subject. 
From the result of his researches he concluded that two sulphates 
of the copper-magnesium group often crystallise together in very 
simple ratios when they are dissolved together in equivalent propor- 
tions, the solution allowed to evaporate spontaneously, and the crystals 
collected fractionally as they are formed (“Ueber das Verhaltniss 
in welchem isomorphe Korper zusammen krystallisiren und den 
Einfluss desselben auf die Form der Krystalle,” Pogg. Ann., xci. 321). 
