# The Dictionary Of Photography

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

 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. 650