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Water-marks |
Weighing and Measuring |
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In preparing distilled water, that first coming over (say about one-twentieth) should be rejected, as liable to contain ammonia and volatile impurities. Another form of still, and one which involves still less special fitting or construction is shown in |
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Fig. 133.
fig- l33i tne constituents being a tin can, A, in which the water is boiled, a bent glass tube (see Glass Working) fitted to a by means of a perforated cork. Another tin can, b, into which the bent tube passes loosely, stands in a saucepan containing cold water.
Water-marks, reproducing by Photography. See Filigrane.
Weighing and Measuring. - In ordinary photographic opera-tions extreme accuracy in weighing and measuring is not required; and as regards balances, an ordinary shopkeeper's pair of scales will serve for the larger quantities, and a pharmacist's dispensing scales for smaller quantities. The larger scales are best of the platform type, in which the beam is below the pans, and they may conveniently weigh up to about 7 lbs., but they should give a clear indication of a difference of 10 grs. The smaller scales should, if practicable, be of much better quality than the cheapest kind sold; indeed, it is hard to obtain a satisfactory dispensing balance with drawer and stand for less than £1 5^. or £1 ioy., although a cheap substitute may be had in a box, and without the stand, for 2s. 6d. or 3$. A good pair of dispens-ing scales will indicate
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