Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed / by Rubert Boyce.

  • Kenwood, Henry R. (Henry Richard), 1862-1945.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed / by Rubert Boyce. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    in general use in France and Germany. In the estima- tion of organic matter, however, it seems preferable— dealing as we are with such small amounts—in order that the results shall represent whole numbers, to take larger quantities of the water, and to return the estima- tions as parts per hundred million. The findings of the whole analysis will then be appropriately expressed in terms of either parts per hundred thousand or parts per hundred million. It appears advisable, nevertheless, to make one ex- ception in the case of a quantitative examination of the poisonous metals, and to express these—in those uncom- mon cases where they exist—in terms of grains per gallon, since they are almost invariably thus referred to in this country. Such then will be the quantitative expressions used throughout this book. Where, however, the terms em- ployed are other than those to which the reader has grown familiar, he should convert them into such before attempting to form an opinion of the water. The process is a very simple one ! Parts per million are obviously converted into parts per loo million by mul- tiplying by loo, or by moving a decimal point two places to the right, and parts per hundred thousand are converted into parts per million by multiplying by ten ; but the conversion of grains per gallon to parts per 100,000 is not so apparent. Supposing a report reads chlorine 2*8 grs. per gal- on, how many parts per 100,000 will this represent ? Now there are 70,000 grains in a gallon. ,, ,, 2-8 grains in 70,000 grains, or 2*8 parts per 70,000 parts. .*. as 70,000 : 100,000 : : 2-8 : x (parts per 100,000). Or as 7 : 10 : : 2-8 : x = ^ (parts per 100,000).