. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . s then found by adding to a similar volume ofdistilled water and reagent, a solution which containsknown quantities of the substance, and this is con-tinuously added until the colour is matched (which actof matching is known as titrating). The amountof the substance contained in the amount of the stan-dard solution used, is of course the same as that exist-ing in the solution under analysis. Apparatus Required. 1. A condensing a
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . s then found by adding to a similar volume ofdistilled water and reagent, a solution which containsknown quantities of the substance, and this is con-tinuously added until the colour is matched (which actof matching is known as titrating). The amountof the substance contained in the amount of the stan-dard solution used, is of course the same as that exist-ing in the solution under analysis. Apparatus Required. 1. A condensing apparatus. 2. A boiling flask or retort, most conveniently ofabout a litre capacity. This must be supported upona four footed iron stand across the top of which a pieceof wire gauze has been placed, and then attached to thecondensing apparatus by means of the cork which isperforated by the bent end of the smaller tube, the ex-tremity of which is allowed to project about half an inchbelow the cork into the neck of the bottle [vide figure 25)- 40 LABORATORY WORK. 3. Six Nessler glasses. One of these is representedin figure 25 as catching the condensed vapour. They. 42 c 3O cu o 4-1 O o •2 ^ £ j^ x) O a. a, H 2 are each marked off at a point which indicates the levelto which 50 of water will stand in them, and should wanklyns process. 41 be made of thin colourless glass and of precisely similardiameter. 4. A white porcelain slab about six inches square,which is used to facilitate colour comparison. 5. A burette graduated in cubic centimetres andtenths of cubic centimetres, fixed upon a stand andfitted with a glass stop-cock which regulates the de-livery with delicacy. 6. A glass measuring flask for 500 cubic centimetres(500 ) of water. Chemical Reagents. 1. A standard solution of chloride of ammonium,made to the strength that i contains o-oi milli-gramme of ammonia. 2. Nesslers reagent. This consists of a solution ofpotassium iodide and the periodide of mercury in
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisherphiladelphiablakis
