Food : its adulterations, and the methods for their detecton / by Arthur Hill Hassall.

  • Arthur Hill Hassall
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: Food : its adulterations, and the methods for their detecton / by Arthur Hill Hassall. Source: Wellcome Collection.

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    i say 100 feet of chalk, would be very much hetter filtered than any water iVhich finds its way to the Thames. , ■, . , , ' 6292 You conclude that it is a very difficult thmg to get rid of sewao-e matter by rimuing water ?—I do. That portion of it which : remains''undecomposed after its passage thi-oiigh the servers oxidizes 1 Tvith extreme slowness. ' 6297. Did I rightly understand you to say that you cannot dis- I tinc^uish in those cases whether it (theorganic niti-ogen) is_ derived from •vegetable matter or from animal matter?—I have said that until I recently it had been impossible to distinguish between the two ; but : that now I considered that the proportion between the carbon and the : nitrogen in the two cases afiorded a basis fi'om which we could in many : instances decide. ' 6328. It would seem that you cannot very well refer the presence of niti-ates and nitrites in the water exclusively to previous sewage con- tamination,—[After alluding to the presence of materials in rain-water which may ftu-nish a small quantity of nitrates and nitrites, Dr. Franklaud observed] : But it is a remarkable circumstance that waters which it is well known cannot be contaminated by manm-e or by sewage, never do contain those nitrates in. a proportion bringing them max to the point of contamination. ' 6-S72. Then you do not accept the theory that sewage discharged at point A, and travelling down the river, is so oxidized as it passes a distance of six or seven miles, and is so entirely destroyed, that its orio-inal elements are not to be found; but it is converted into some other substance or substances which are not detrimental to human health ?—I believe that it is by no means a generally true proposition.' Dr. Odling's evidence was to -^he following efiect:— ' Q. 6448. Have you found in those examinations of the Thames water the presence of sewag-e not decomposed ?—I have not. ' 6461. Has yom- attention been directed to the important principle of the self-purifying process which is going on in rivers running at a given velocity?—Yes, it has. There may be great difference of opinion as to the degree to which that self-purification takes place, but that it does take place to a very considerable extent I think is imdeniable. ' 6462. Is it your opinion that those (nitrates) which have been found in chaUc water are due to sewage ?—It is a point upon which there is no positive evidence, but I am inclined to think that it is not 80, for we find them distributed so irregularly. For instance, the deep- well water at Trafalgar Square and the deep-well water from the green sand and the lower chalk, all over London, is nearly free fi-om nitrates and nitrites, whereas the water of equally deep wells elsewhere in the chalk is found to contain very considerable quantities of nitrates and nitrites. The deep-well water from nearly all formations has been found to contain nitrates. Then, moreover, a proportion of the nitrates which the sewage itself undoubtedly does furnish in one case is destroyed, and in another is not; and so far as the history of the water is con-
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