17, 6 Trelease: Salt Requirements of Wheat Plants 535 
Thus the solutions here considered are four-salt solution’s, and 
they are similar in their general make-up to the other four-salt 
solutions already employed by Tottingham. It will be seen that a 
solution made up of monopotassium phosphate, calcium nitrate, 
magnesium sulphate, and potassium chloride may be derived 
from the proper one of Shive’s three-salt series by the addition 
of potassium chloride. These four salts have been employed 
in Nobbe’s solution in a single set of proportions and in the 
so-called Detmer’s solution in another set of proportions, as 
pointed out above. The present study aimed primarily to em- 
ploy these four salts in various proportions, the total concen- 
tration of the solution remaining the same. The effects of 
different total concentrations with a constant set of salt pro- 
portions was also studied to some extent. 
Culture solutions . — The culture solutions, whose compositions 
are given among the other data of the individual experiments, 
were prepared from analyzed chemicals 33 and water obtained 
from a “Barnstead” still. Each salt was dissolved separately, 
and the exact concentration of the resulting solution was de- 
termined by chemical analysis (except in the case of potassium 
chloride). This procedure is especially necessary for solutions 
of calcium nitrate and of magnesium sulphate, because these 
salts contain amounts of water of crystallization that vary 
between wide limits, and because they are rather readily decom- 
posed by heat. Upon dilution to convenient volume-molecular 
concentrations, 34 these solutions became the “stock solutions” 
from which the various culture media were prepared. The 
stock solutions were stored (never longer than one month) in 
cork-stoppered glass bottles. 
Ferric phosphate (used as a source of iron) was prepared 
from a ferric nitrate solution by precipitation with a one-fourth 
molecular solution of monopotassium phosphate. The precipi- 
tate was obtained in a finely divided condition by using cold 
solutions and by constantly stirring while the potassium salt 
was added. After thoroughly washing the precipitate, it was 
shaken with sufficient water to form a suspension containing 
approximately 0.0022 gram of ferric phosphate, or 0.0008 gram 
of iron, in each cubic centimeter. 
“ The potassium chloride was the Baker and Adamson Chemical Com- 
pany’s “analyzed” salt; the other salts were the J. T. Baker Chemical Com- 
pany’s “analyzed” salts. 
84 By volume-molecular concentration is meant the number of gram 
molecules contained in each liter of solution. 
