For example: if a plate exposed to the vapor of iodine be perfectly coated in sixteen seconds, and then exposed to an accelerator, (not having iodine in its combination) receives its coating in four seconds, it will be found that a proper proportionate coating cannot be preserved by adopting, a proportion of time, but on the contrary, the time will diminish; for exposure over the accelerator, as in the above example, if it be desired to coat the plate with twice as much iodine as in the above example, the time would be, over iodine thirty-two seconds, and over the accelerator (to possess a proper proportion) from six to seven seconds.

Hence it is that many inexperienced operators, when wishing to vary their usual manner of coating, fail in producing a favorable result.

They coat calculating a proportion of time when they should not.
Dry Quick, No.

2 .-- Bromide of Lime and Magnesia .-- To one quart of hydrate of lime add one quart of magnesia, and mix them well together; add bromine same as in preparing bromide of lime; coat the same as over dry quick No.1.

This combination produces very uniform results, and is worked with much success by beginners.
Chloro-Bromide of Lime .-- To the bromide of lime add chloride of bromine until the mixture becomes a pale yellow color, resembling sulphur.