METOL - HYDROQUINONE (M ETOL QUINOL) A mixture of metol and hydroquinone is a popular developer, being clean in working and suitable for most kinds of plates and bromide and gaslight papers. It is sometimes known as metol-quinol, quinol being another name for hydroquinone. Scores of one, two, and even three solution formulae have been given, but there is very little difference between them. Taking a dozen of the best known formula?, the average one-solution developer is as No. 3 in the table given in the preceding article, this developer being ready for use and of the correct strength for negatives, lantern plates and gaslight papers, but when used for bromide papers an equal amount of water is required. The hydroquinone and metol are not in equal proportions, but many prefer to have the hydro quinone in excess, the metol being the more expensive of the two. The proportions may be altered to suit the temperature, it being advisable to have more metol than hydroquinone in cold weather, because hydroquinone is apt to work very slowly in winter, especially when sodium carbonate is used, and, moreover, is apt to crystallise from its solution. Foramlm for two
and three-solution developers are given below : Two-solution A. Metol . . . 4o grs. 4.6 g.
Sodium sulphite . 120 „ 14 ,, Potassium bromide. ro „ P2 „ Hydroquinone . 5o „ 6 „ Water . . . 20 oz. 1,000 ccs.
B. Potassium hydrate 4o grs. 4.6 g.
Water . . . 20 oz. 1,000 ccs.
For use, take equal parts of each.
Three-solution A. Metol . . . 100 grs. I 1.5 g.
Sodium sulphite . 30o „ 34'5 ,, Water . . . 20 OZ. 1,000 ccs.
B. Hydroquinone . loo grs. 11•5 g.
Citric acid . . 25 „ 3 Water . . . 20 OZ. 1,000 CCS.
C. Potass. carbonate . r oz. 55 g.
Water . . . 20 „ 1,000 ccs.
Normally, use r part each of A and B and 2 parts of C ; in cases of over-exposure, add potassium bromide, and for under-exposure increase the proportion of C.
When making up solutions of metol, sodium sulphite, and hydroquinone, always dissolve the chemicals in the order given.