Use.—Coat over the iodine to a rose red and then over this mixture to a purple or slate; recoat over the first about one fourth as long as first coating.
Gurneys American Compound.—Of this compound there are two combinations, one for use, when the temperature of the atmosphere is above 65 or 70 deg., and the other at a lower temperature. The first is called No. 1, the second No. 2.
No. 1 is prepared by placing hydrate of lime in a bottle, say to three quarts of the hydrate of lime, add one ounce of pulverized burnt alum, and as much chloride of lime as can be put on a quarter of a dollar, and from 15 to 30 grains of dry pulverized iodine, or enough to change the color of the hydrate of lime, to the slightest possible tinge of yellow. There had better be less than carry the color to a deeper shade. The object of using the iodine is to form a compound with bromine that is not so volatile as the bromine itself. No matter how little iodine is combined with the bromine, the vapors possess their relative proportion; hence, only enough iodine to prevent “flaring,” or as it is often termed a “scum-coating,” is used. The iodine should be thoroughly combined with the lime, which will take about one or two days. Should add bromine the same as in bromide of lime, until the compound assumes a light red color.
No. 2 is prepared in the same manner as No. 1, except the addition of the iodine, which is omitted.
Use.—No. 1. Coat over the iodine to a bright yellow color, then over the compound, No. 1, to red color, recoat over iodine, about one sixth as long, as the time occupied in first coating.
No. 2. Coat over iodine same as above, except recoat over the iodine about one fourth to one half as long as first coating.
Dry Quick, No. 1.—Bromide of Lime and Starch.—The following compound forms an excellent accelerator, and is used by many. It is claimed for this preparation, that it will hold the bromine longer than others where starch is not employed. As regards this claim we do not think it can be substantiated. Our experience in practice has led us to the conclusion that there is no great difference as respects durability, but there is some little difference as regards the tone of the impressions produced by its use.
To one quart of hydrate of lime add one quart of finely pulverized starch. To this mixture add bromine, until it assumes a deep yellow or pink color.
Starch may be added to any of the dry mixtures.
Use.—Coat over the iodine to a deep yellow, then over this quick to a red color, recoat about one sixth of the time of first coating.