1900] CHANGE OF FORM 1N GREEN ALG# 293 
small, loosely covered glass dishes - containing from 5° to 10° 
of solution. The cultures stood on glass shelves close against 
the panes of an east or west window, and were always shaded 
from the direct rays of the sun by a curtain of white muslin, 
which was left constantly in position during the high tempera- 
tures of the summer months. Examination of cultures was 
made from time to time by transferring the dish with its con- 
tents directly to the stage of the microscope and using an 
objective of medium low power. 
The culture media used were modifications of the well-known 
fluid of Knop,3 consisting of the following salts: calcium nitrate, 
four parts ; magnesium sulfate, one part; potassium nitrate, one 
part; di-potassium acid phosphate, one part; iron, a trace. 
Owing to the extreme weakness of the solutions to be used, it 
was deemed advisable to secure at the outset, as nearly as might 
be, the exact proportions of the constituent salts here given, and 
to this end the following method was adopted. By reference to 
tables of the physical properties of solutions,* the corresponding 
Specific gravity and gram-molecular strength of solutions of 
the first three of the above salts were found. By the use of these 
fata a stock solution of each of these compounds was made up, 
“ga contained a specific number of gram-molerwies ea 
ae Sa specific gravity bottle was used in these pn 
Surth we was always taken into account. For the 
in the list data could not be found; therefore it was 
‘ae in solution from normal solutions of phosphoric acid and 
oY droxid. The physical constants for these ae . 
a. eae of this method for producing K, re pe 
Retite f * ‘umetric analysis and found to is ae t 
a . oe of a normal solution of this salt so made es 
throughout € 1.13207 at 15°C. Redistilled water was us 
all of the work. 
he stock solutions thus prepared were kept in flasks tightly 
with rubber; their specific gravity was taken from 
8,G.: op. cit., p. 8 
tE. g. ; ; 
bridge, . given by WHeTHaM, W.C.D., Solution and Electrolysis, 
215. Cam- 
