1888.] Prafulla Chandra Ray on Co;pper- Magnesium Group. 269 
tallising dishes. Crystallisation did not in most cases go on 
continuously as the liquid evaporated, hut commenced somewhat 
abruptly, and having once commenced proceeded pretty rapidly. 
After a time crystallisation ceased altogether or nearly so, and at this 
stage the “ crop ” was collected. After a comparatively long pause, 
crystallisation recommenced and a second “crop” separated out. 
The second crop differed generally in composition from the first. 
Xot unfrequently, however, the end of the first crystallisation or 
crop overlapped the beginning of the second, so that a heterogeneous 
deposit of crystals of indefinite composition occurred. The amount 
of such heterogeneous deposits was usually small compared with 
that of the crops proper. The deposit or crust which adhered to 
the walls of the crystallising dish was rejected, as I found them to 
be of a different composition from the main mass of the crystals. 
For each case the combined weights of the sulphates taken was 
never less than 35 grammes, and the crops collected amounted 
usually to from 3 to 5 grammes. The crystals thus obtained were 
pulverised and air-dried. 
Detailed Remarks on each Preparation. 
I. Cobalt-Mckel-Potassium Sulphate. — One crop of this pre- 
paration was collected in accordance with the general plan. The 
crystals belonged to the rhombic system, and were of a pale blue 
colour. Examined by means of a Haidinger’s prism, they were 
found to be dichroic, as remarked by Thomson. 
The cobalt was separated as “Fischer’s salt,” which was then 
dissolved in hydrochloric acid, and the excess of acid got rid of by 
evaporatiou. From the solution the cobalt was precipitated by pure 
caustic soda. The hydrated oxide was dried and ignited in a 
current of hydrogen, according to Rose’s method. The reduced 
metal was thoroughly washed with hot water, to remove alkalies 
which adhere so tenaciously to the oxides of cobalt and nickel, and 
was then again heated in a current of hydrogen and weighed. 
The nickel in the filtrate was precipitated by pure caustic soda, and 
estimated as the protoxide. 
II. Zinc-Manganese-Ammonium Sulphate. — In this preparation 
the component sulphates were mixed together as above. The 
first crop consisted of limpid and transparent rhombic prisms. In 
