The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Water-marks
Weighing and Measuring
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
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 indicateof a grain, and will turn immediately or decidedly with a grain; and its use effects a considerable saving of time as compared with those that are less sensitive. Continually taking down and rehanging tends very much to damage and wear down the knife edges; hence it is best to
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