362 PHOTOGRAPHIC FACTS AND FORMULAS 
1.5 0.72 11 ‘il Since 
2 0.96 115 Bie 
yale LZ iz 5.76 
3 1.44 Leo 6.0 
Me 1.68 13 6.24 
4 1,02 13.9 6.48 
4.5 2.16 14 6.72 
5 2.4 14.5 6.96 
op 2.64 nny. 72 
6 2.88 15.5 7 44 
6.5 3.12 16 7.68 
i 3.36 16.5 7.92 
75 3.6 17 8.16 
8 3.84 175 8.4 
8.5 4.08 18 8.64 
? 4.32 18.5 8.88 
9.5 4.56 19 9.12 
10 48 19.5 9.36 
20 9.6 
Approximate rule to convert English weights and measures 
into metric: 
1. Call the new volume of solvent 1000 ccm. 
2. If any of the ingredients run to ounces, take their ratio 
to the solvent, and write down the same ratio to 1000 in 
grams. 
3. Divide each grain item by half the number of ounces, 
and write the result down in grams. 
PERCENTAGE SOLUTIONS.—Some dispute has prevailed as 
to the exact meaning of “x per cent solution,” but in photo- 
graphic practice it means x parts in 100 parts of the total bulk 
of solution. As most chemicals are sold by the avoirdupois 
ounce of 437.5 grains, and liquids are measured by the ounce 
of 480 minims, some confusion has arisen. The following 
