1920] 
DUGGAR—H-ION CONCENTRATION AND NUTRIENT SOLUTIONS 3 
tageously applied by Tottingham in his elaborate account of 
nutrient solutions, and by Shive, McCall, and others in intensive 
analyses of physiological balance. The effect of variation in 
H-ion concentration may be approached finally in the same way. 
In this rather general survey of certain aspects of the subject, 
however, it has seemed that the factors are for the most part too 
complicated for most economical treatment by this method 
alone. 
TECHNIQUE AND MATERIALS 
In the earlier work I selected for comparative studies on the 
influence of variation in H-ion concentration two solutions only: 
namely, a slight modification of Shive's R;C2, considered his 
best solution of optimal concentration, and a much modified 
Crone solution developed in this laboratory. Later there was 
added the R.C, solution of Livingston and Tottingham, and 
ultimately some other combinations which seemed worthy of 
consideration. 
The partial volume-molecular proportions of the particular 
Shive solution employed are as follows: KH+PO,, 0.0180; Ca 
(NO); 0.0052; and MgSO,, 0.0150. Ferric phosphate in small 
amount is added, the partial concentration being 0.0044 gm. per 
liter of solution. This insoluble salt is used at such a low con- 
centration that its presence as a precipitate is scarcely percept- 
ible. Ihave employed the same salts in the same proportions, 
except that ‘‘soluble ferric phosphate" has been substituted for 
the insoluble iron salt in all cases not otherwise indicated. This 
substance is described as consisting of scales of ferric phosphate 
with sodium citrate, possibly as a single salt. The exact molee- 
ular composition of this iron-furnishing substance is unknown. 
From the description in the National Standard Dispensatory 
(1905) it will be seen that it is commonly made by the addition 
of 50 gms. ferric citrate and 55 gms. sodium phosphate, unef- 
floresced, to 100 cc. distilled water. It is barely possible that 
four salts are present, namely, sodium and ferric phosphate and 
sodium and ferric citrate. This salt combination possesses the 
advantage of solubility to a high degree, yielding what appears 
at first to be a true solution but seems in reality a colloidal solu- 
tion of high dispersity. Used in such extreme dilution as 
