Early Work In Photography
A Text-book For Beginners

96 Early Work in Photography. .The liter (= 1,000 c.c.) is the unit of the decimal fluid measure, and weighs 1,000 grams. One c.c. equals 17 minims English. The metric system has been adopted by many nations, the English excepted. In America its use is optional, but is legalised by Congress. ,.. European formulæ are expressed in grams and cubic centimeters; these may be made up in any quantity by mounts as " parts ”—either grains or drams r fluid). The better plan, however, is to buy its and cubic centimeter graduates and counting the (apothecaries a set of metric weights and cubic centimeter graduates sun mix the formulæ at once without calculation or confusion. Without doubt, the metric system is the only one for scienti- fic use. English Weights and Measures used in Photography. Apothecaries' Weight. By which photographic førmulæ are generally compounded. 1 grain = the unit 20 grains = 1 scruple . 3 scruples = 1 dram ( 60 grains) 8 drams = 1 ounce (= 48o grains) 12 ounces = I pound ( 5760 grains) The measure employed for liquids is as follows: 1 minim 4 the unit 60 minims = 1 dram _8 drams = i ounce • 20 ounces = 1 pint Avoirdupois weight, by which chemichlsare sold. I grain = the unit 2711/32 grains = 1 dram 7 crains) 16 drams = I ounce (— 437a grains) 16 ounces = I pound (= 7,000 grains) Pyro. Pyro-soda Developer. An excellent pyro-soda developer can be made in three solutions as follows: „ Sulphuric acid, C.P. 60 minims Water, .. 40 ounces add Pyro ..480 grains Carbonate. (Sodium carbonate .. 6 ounces ( 2880 grs.) are 1Water, to .. 40 ounces , 00 Sulplute. (Sodium sulphite .. 6 ounces (— 2880 grs.) • 1 Water, to .. 40 ounces Sul