STEINBERG: ZINC SULPHATE AND ASPERGILLUS NIGER 289 
The compounds employed in the preparation of this solution were 
water redistilled through glass; Merck’s “ Reagent" ammonium 
nitrate and magnesium sulphate; Kahlbaum’s “Zur anal.” 
magnesium sulphate; and Baker’s “Analyzed” potassium phos- 
phate, ferric sulphate, and zinc sulphate. The cane sugar used 
is that sold under the proprietary name of ‘‘Crystal Domino" 
sugar. This solution was prepared as needed. 
The flasks used were: 200 c.c. Jena and 150 c.c. Pyrex Erlen- 
meyer's; and 250 c.c. Kavalier Bohemian Florence flasks. "They 
were cleaned by rinsing with concentrated sulphuric acid, tap- 
water, lastly distilled water, and inverted to drain dry. Тһе pre- 
caution was taken of reserving part of the flasks for zinc-free 
cultures and part for zinc cultures only, though this performance 
is unnecessary, as the following indicates: 
I. ON THE EFFICIENCY OF THE METHOD FOR CLEANING THE CUL- 
TURAL FLASKS 
Pfeffer solution: water redistilled through glass; ‘‘Crystal 
Domino” sucrose; ХН. ХО: (Merck) ;. KH2PO, (Baker); MgSO,.- 
7Н.О (Kahlbaum). Temperature 30-31? C. Period of growth 
7 days. No zinc added. Pyrex flasks. 
Flasks reserved Flasks reserved 
for zinc-free cultures for zinc cultures 
0.924 grams* 0.283 iun 
о ЫЫ 0.26 
„Зат г 0.313 " 
0328. ^ GZ e e 
0:355 oc: ggs ди 
олак ет” 
The flasks in the second column were previous to this ехрегі- 
ment used three consecutive times for cultures containing IO 
mg. Zn/L. and were cleaned as usual. 
Zinc was added where indicated to the entire solution used 
in the preparation of cultures having the same concentration of 
this heavy metal and not to the individual flasks. The stock solu- 
т * High yield, due probably to the accidental lokzoductdod: of zinc. This valüe 
not included in the average. In at least one case it was noted that the same Р 
flask consistently gave cultures having a high yield, though the addition of zinc 
"was omitted. 
