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 numbers taken from the tables simply require the altering of the position of the decimal point.
The following may be useful for obtaining an approximate weight: -
It has become somewhat general lately to give formulae in parts, and this, though not strictly accurate,, unless everything be taken by weight, as is common in chemical laboratories, gives a basis for a somewhat convenient method of approximately translating metric measures into English weights and measures by assuming a gramme and a cubic centimetre to be identical; which, however, is only approximately true even when the cubic centimetre is a measure of water or of a fluid having the same specific gravity.
Frequently we find a solution spoken of as u a 48-grain bath," " a 60-grain bath/' etc.; and this means that each ounce of the solution contains 48 or 60 grains of the salt.
Ten per cent, solutions are, again, somewhat of a trouble to some, and the trouble arises from the fact that we are in the habit of measuring liquids, and that the avoirdupois ounce con-tains only 437*5 grains, whilst a fluid ounce contains 480 minims. To make a 10 per cent, solution of any salt we proceed as follows : - Let us take, for instance, an ounce of pyro., and it is required to make a 10 per cent, solution; that is to say, we require a solution, every 10 minims of which shall represent 1 grain of pyro.; then, having 437*5 grains of pyro., the total bulk of the solution will be 437-5 x 10 = 4375 minims = 9 oz. 55 minims. Any other strength solution may be made in the same way, but such a solution is not a 10 per cent, solution in any real sense of the term.