The chemical examination of water, sewage, foods, and other substances : by J. E. Purvis and T. R. Hodgson.

  • Purvis, John Edward.
Date:
1914
Catalogue details

Licence: In copyright

Credit: The chemical examination of water, sewage, foods, and other substances : by J. E. Purvis and T. R. Hodgson. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

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    Concentrated sulphuric acid free from nitrates. Potassium nitrate solution. 0*0749 gram of potassium nitrate is dissolved in 1000 c.c. of water; 25 c.c. of this solution contain oooi gram of 'N>Ot. To determine the strength of the indigo solution, 25 c.c. of the potassium nitrate solution are placed in a small flask together with 25 c.c. of the concentrated sulphuric acid, and the indigo solution is run in from a burette, with constant shaking, until a permanent green colour is obtained ; a second experiment is then made with a further 25 c.c. of the potassium nitrate solution, but in this case the whole of the indigo solution required in the first experiment is run in at once and the mixture well shaken. Should the green colour not be permanent, further quantities of the indigo solution are added drop by drop until the permanent colour is obtained. From the second experiment the number of c.c. of indigo solution corresponding to oooi gram of NqOs is obtained ; this should be from 7 to 9 c.c. The process for the sample of water is carried out exactly as described above, 25 c.c. of water being used instead of the potassium nitrate solution. The method is very rapid, but the results obtained are not absolutely accurate as they are affected by the presence of easily oxidizable organic matter, and also by the rapidity with which the determination is carried out. When animal organic matter containing nitrogen is oxi- dized, nitrates are ultimately formed; the presence, therefore, of large quantities of nitrogen in the form of nitrates in a water indicates past pollution, unless it can be shown that such nitrates are obtained from the rocks in the well. For example, waters from the chalk contain as much as 07 part per 100,000 of nitric nitrogen. Nitrogen as Nitrites. (a) Solutions required: Metaphenylene-diamine solution. Weigh out 2 grams of metaphenylene-diamine hydrochloride ; dissolve it in distilled water and make up to 100 c.c.