884 Mockeridge. - Some Conditions influencing the Fixation of 
in this respect. Appended is an analysis of the slag which, together with 
samples of the material, was furnished by the courtesy of the Manager 
of the Chemical Works— late H. and E. Albert. 
Silica ....... 6*95 per cent. 
Alumina 5-42 „ 
Ferrous oxide of iron .... 4-83 „ 
Ferric „ >, 8-49 
Lime ...... 47-02 „ 
Phosphoric acid 18-88 „ 
(Citric acid soluble phosphoric acid = 15-74 „) 
Manganese ...... 2-30 ,, 
Magnesium oxide . . . . 5 ,][ 5 » 
Sulphur ...... 0-96 ,, 
Total iron = 6-89 ,, 
The proportion of slag required to induce a maximum fixation of 
nitrogen is 0-4 per cent. 
This solution, with basic slag as the neutralizing agent, contains all the 
ingredients which Mme Krzemieniewski states are essential to the develop- 
ment of Azotobacter , besides the iron which Omeliansky and Ssewerowa, 
and more particularly Remy and Rosing, find to be so important, and the 
aluminium and silicon which the experiments of Kaserer prove to be so 
beneficial. Mme Krzemieniewski states that the minimum amounts of the 
elements requisite for the consumption of 1 grm. of dextrose are potassium 
0-38 mg., calcium 0-36 mg., magnesium 0-35 mg., phosphorus 2-46 mg., and 
sulphur more than 0-49 mg. These requirements are fulfilled by the 
medium the use of which is here advocated, and the results obtained 
appear to be in accordance with those of the investigators mentioned. 
Although nitrogen-fixation can, and does, under favourable conditions, 
proceed until the food material is completely exhausted, yet the most active 
fixation of nitrogen in the small 50 c.c. cultures used in the laboratory 
is obtained during the course of the first week, possibly owing to some 
depressing influence which the accumulation of the products of their vital 
activity may exert upon the organisms. 
The yield of combined nitrogen per unit of carbohydrate consumed is 
apparently not influenced by the depth of the layer of liquid to such an 
extent as to warrant the use in all cases of the minimum quantity, and, for 
the purposes of experiment in the laboratory, a volume of 50 c.c. of solution 
in a 300 c.c. Erlenmeyer flask gives a layer sufficiently well aerated to ensure 
a good fixation. The best results are evidently not obtained by the supply 
of only very small amounts of carbohydrate food material, but, once a good 
growth is obtained, the yield of nitrogen appears to be practically propor- 
tional to the amount of food supplied. The use of fairly thin layers of 
