468 Philippine Journal of Science 1920 
content furnished on the label being taken as a basis for pre- 
paring the solution in each case. Doubtless some errors were 
introduced by this procedure. The study was to be only prelim- 
inary in character, however, and this kind of work always 
involves many unknown and uncontrollable conditions, some of 
which are surely more influential in determining the growth of 
the plants than are the errors introduced by empioying the manu- 
facturers’ data on water content, so that special analyses (with 
their relatively great consumption of time) seemed undesirable 
in the present case. It was at first intended that samples of 
the single-salt stock solutions should be subjected later to quan- 
titative determinations, in order to obtain their actual concen- 
trations, but time was finally lacking for this. It is undoubtedly 
better, in work of this kind, to make up the solutions and then 
determine their concentrations by analytical methods, than to 
attempt to dry the salts to a known water content before dis- 
solving. The errors here considered of course apply only to 
calcium nitrate, ammonium sulphate, and monocalcium phos- 
phate; the other two salts are practically dry as they come on 
the market. 
The ferric phosphate (FePO,) used was prepared according 
to the procedure of Shive and Tottingham; that is, the ferric 
nitrate [Fe(NO,),] was allowed to react with monopotassium 
phosphate (KH,PO,), forming the precipitate, which was then 
thoroughly washed with distilled water. The precipitate di- 
vides very finely and settles to the bottom of the container only 
after considerable time. When this material was needed for ad- 
dition to the culture bottles (when new cultures were to be 
started or solutions were to be renewed) the bottle containing 
the precipitate and its supernatant water were thoroughly shaken 
so as to give a uniform suspension. Five cubic centimeters of 
this suspension, containing about 11 milligrams of ferric phos- 
phate, were added to each 250 cubic centimeters of culture S0- 
lution. The slight further dilution resulting from this addition 
of 5 cubic centimeters of water to each 250 cubic centimeters 
of culture solution was regarded as insignificant. 
The distilled water used was that of the laboratory, derived 
from a Barnstead still, the same as was used by Hawkins,” 
Shive (1915), and Tottingham (1914). 
_™ Hawkins, Lon A., The influence of calcium, magnesium and potassium 
nitrates upon the toxicity of certain heavy metals toward fungus spores, 
Physiol. Res. 1 (1913) 57-92. 
