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Art. XXIX.—The Fixation of Atmospheric Nitrogen by Nitrogen-fixing Bacteria in Certain Solutions.
[Read before the Philosophical Institute of Canterbury, 11th December, 1907.]
This paper is the record of the work carried out preliminary to soil experiments to determine under what conditions of alkalinity and acidity nitrogen-fixing bacteria will fix atmospheric nitrogen.
A solution of 1 gram each of cane-sugar, ammonium-sulphate, magnesium-sulphate, and potassium-sulphate in 1 litre of water was prepared; to 10 cubic centimeters of this solution 100 milligrams of cotton-wool containing the bacteria were added. This was then rendered acid or alkaline. The degree of acidity or alkalinity are expressed as parts of calcium-oxide per million, this being the usual method of expressing these results in soil-determinations.
The experiments were carried out in Kjedahl digestion flasks. At the end of the experiment it was merely necessary to add mercury and sulphuric acid, and proceed with the nitrogen determination as in other Kjeldahl estimations.*
| Nitrogen found. | Nitrogen fixed. | |
| Days. | Mg. | Mg. |
| 0 | 2.1 | |
| 3 | 2.7 | 0.6 |
| 7 | 3.4 | 1.3 |
| 10 | 4.2 | 2.1 |
| 14 | 5.1 | 3.0 |
| 21 | 6.7 | 4.6 |
| 28 | 8.8 | 6.7 |
[Footnote] * Bull. No. 81, Bureau of Chemistry, U.S.A. Dept. of Agric., p. 152.
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[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
| 1. | 2. | 3. | ||||
|---|---|---|---|---|---|---|
| Nitrogen found. | Nitrogen fixed. | Nitrogen found. | Nitrogen fixed. | Nitrogen found. | Nitrogen fixed. | |
| Days. | mg. | mg. | mg. | mg. | mg. | mg. |
| 0 | 2.1 | 2.1 | 2.1 | |||
| 3 | 2.4 | 0.3 | 2.2 | 0.1 | 2.1 | |
| 7 | 3.1 | 1.0 | 2.6 | 0.5 | 2.2 | 0.1 |
| 10 | 3.9 | 1.8 | 2.9 | 0.8 | 2.2 | 0.1 |
| 14 | 4.3 | 2.3 | 3.0 | 0.9 | 2.4 | 0.3 |
| 21 | 5.6 | 3.5 | 3.2 | 1.1 | 2.6 | 0.5 |
| 28 | 6.7 | 4.6 | 3.6 | 1.5 | 2.8 | 0.7 |
Experiment 1. Acidity required, 254 parts of CaO per million to neutralise solution.
Experiment 2. Acidity required, 646 parts of CaO per million to neutralise solution.
Experiment 3. Acidity required, 1050 parts of CaO per million to neutralise solution.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
| 1. | 2. | |||
|---|---|---|---|---|
| Nitrogen found. | Nitrogen fixed. | Nitrogen found. | Nitrogen fixed. | |
| Days. | Mg. | Mg. | Mg. | Mg. |
| 0 | 2.1 | 2.1 | ||
| 3 | 2.8 | 0.7 | 2.6 | 0.5 |
| 7 | 3.7 | 1.6 | 3.2 | 1.1 |
| 10 | 4.8 | 2.7 | 4.1 | 2.0 |
| 14 | 5.5 | 3.4 | 4.9 | 2.8 |
| 21 | 7.1 | 6.0 | 6.5 | 4.4 |
| 28 | 9.3 | 7.2 | 8.5 | 6.4 |
| 3. | 4. | |||
| Notrogen found. | Nitrogen fixed. | Nitrogen found. | Nitrogen fixed. | |
| Days. | Mg. | Mg. | Mg. | Mg. |
| 0 | 2.1 | 2.1 | ||
| 3 | 2.4 | 0.3 | 2.3 | 0.2 |
| 7 | 2.9 | 0.8 | 2.5 | 0.4 |
| 10 | 3.8 | 1.7 | 2.9 | 0.8 |
| 14 | 4.5 | 2.4 | 3.1 | 1.0 |
| 21 | 6.1 | 4.0 | 3.7 | 1.6 |
| 28 | 7.8 | 5.7 | 4.2 | 2.1 |
| Experiment 1. Alkalinity equals 254 parts of CaO per million. |
| " 2. " 646 " |
| " 3. " 1,050 " |
| " 4. " 1,400 " |
It will be seen from the above that the bacteria fix nitrogen in the greastest quantity when the media are neutral or slightly alkaline. In slightly acid media the nitrogen is fixed in less
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quantities, while when the acidity is 1,050 parts per million the fixation is relatively small. The fixation also decreases as the alkalinity increases over 254 parts per million.
For permission to publish these results I have to express my thanks to the general manager of the Christchurch Meat Company (Limited), in whose laboratory much of the work in connection with this paper was carried out.