The combined toning and fixing bath consists essentially of five parts— (1) water, the solvent; (2) a soluble salt of gold, such as gold chloride; (3) the fixing agent, sodium thiosulphate; (4) a compound which will readily combine with "nascent" sulphur—i. e., sulphur as it is liberated—this is usually a soluble lead salt, such as the acetate or nitrate, and (5) an auxiliary, such as a sulphocyanide.

The simplest bath was recommended by Dr. John Nicol, and is as follows: Sodium thiosulphate. 3 ounces

Distilled water....... 16 ounces

When dissolved, add

Gold chloride. ... 4 grains Distilled water ... 4 fluidrachms A bath which contains lead is due to Dr. Vogel, whose name alone is sufficient to warrant confidence in the formula: Sodium thiosulphate 7 ounces Ammonium sulphocyanide......... 1 ounce

Lead acetate ......67 grains

Alum............. 1 ounce

Gold chloride......12 grains

Distilled water.....35 fluidounces

A bath which contains no lead is one which has produced excellent results and is due to the experimental research of Dr. Liesegang. It is as follows: Ammonium sulphocyanide. ... 1/4 ounce Sodium chloride.. 1 ounce

Alum........... 1/2 ounce

Sodium thiosulphate......... 4 ounces

Distilled water. .. 24 fluidounces

Allow this solution to stand for 24 hours, during which time the precipitated sulphur sinks to the bottom of the vessel; decant or filter, and add

Gold chloride. ... 8 grains Distilled water. .. 1 fluidounce It is curious that, with the two baths last described, the addition to them of some old, exhausted solution makes them work all the better.