The Dictionary Of Photography

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

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Weighing and Measuring
the piston, a blind or imperforate india-rubber teat (obtainable from any druggist) may be used - this being slipped over the upper end of the tube. The confusion which reigns in the photographic world with regard to weights and measures is very notable, arising in great measure from the numerous systems of weights and measures used in different countries. Solid chemicals are sold by avoirdupois weight, whilst many formulae are written in what is called apothecaries' weight. It has been proposed to use the metric system, but at present there seems no likelihood of its coming into general use. As a standard for dry substances the grain has been employed in this Dictionary, and for liquids the minim, or the ounce of 480 minims, except in some cases where a few grains more or less would make no appreciable difference. We do not intend to enter into any arguments as to the desirability or otherwise of a decimal system, but we simply give the tables of weights in general use.
The Old and now Disused Apothecaries' Weight.
20 grains ......... = 1 scruple (3).
3 scruples... ... ... = 1 drachm (5).
8 drachms......... = 1 ounce (3).
The above weights were formerly used by pharmacists tor the compounding of prescriptions, but a simple statement as to grains and ounces is now urged by the Medical Council. The Pharma-ceutical ounce if now the same as the Imperial Standard ounce of 437^ grains, or the Avoirdupois ounce.
Cubic Centimetres (now Millilitres, or nearly so), Minims, and Fluid Drachms.
By virtue of a recent Act of Parliament, followed by a Statutory Order of Her late Majesty in Council (the Weights and Measures [Metric System] Act 1897, and Order in Council of May 19th, 1898. See Statutory Rules and Orders, No. 411 of 1898) the cubic centi-metre has now ceased to be a legal measure of capacity (see Cubic Centimetre), it being replaced by the nearly equivalent millilitre, or one-thousandth of a litre. The following table shows approxi-mately the correspondence of the millilitre with the fluid ounce and the fluid drachm : -