1910] SCHREINER & SKINNER—ABSORPTION AND GROWTH 9 
themselves, are to be used for an experiment, or where plants such as 
cowpeas are used, the wedge must be removed, the seedling put in 
place, and the wedge and rubber band replaced. 
PREPARATION OF PHYSIOLOGICALLY PURE WATER 
It is safe to say that ordinary distilled water, such as is commonly 
found in laboratories, is unsuited for culture experiments. This is 
due to a variety of causes which need not be entered into here, but 
which are discussed in a bulletin by Lrvincston.® Such water, while 
pure from a chemical and physical standpoint, is nevertheless not 
suited for such delicate indicators as plants, which are highly sus- 
ceptible even to very minute quantities of toxic materials. Such 
water can be improved by distillation with strong oxidizing agents, 
such as potassium permanganate in alkaline solution or potassium 
bichromate in acid solution. The far simpler method already 
described by Livincston® has given very satisfactory results in this 
laboratory. In this method the water is purified by shaking it with 
a highly absorptive carbon black, which removes from the water any 
traces of injurious bodies it may contain. Not all carbon black 
possesses this property to an equal degree; the variety used in this 
laboratory is known as the “G Elf” brand, and is prepared on a 
commercial scale by burning natural gas and condensing the finely 
divided carbon on cooled surfaces. It is the same carbon black used 
for the purpose of decolorizing soil and plant solutions in this labora- 
tory. For the present purpose the carbon black is thoroughly washed 
with distilled water as an added precaution, although it is not definitely 
known whether anything is thereby removed from it or not. The 
carbon black is then kept in this moist condition mixed with water 
so as to forma thin paste. About 10 cc. of this paste is added to each 
liter of water which is to be purified, and after shaking the mixture is 
allowed to stand for fifteen to thirty minutes and then filtered through 
an ordinary filter paper into a clean, hard-glass receptacle. Water 
treated thus is very satisfactory for the growth of plants in solution 
cultures. 
8 Livincston, B. E., Further studies on the Lane of unproductive soils. 
Bulletin 36, Bureau of Soils, U.S. Dept. Agric. 1 
