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The result of this bath is a brilliant brown color, what might indeed, perhaps, be best described as a red. Two out of the three prints are much too dark, indicating, perhaps, that this toning bath did not have any tendency to reduce the intensity of the image. The general lesson taught by Clark's experiments is that the sulphocyanide bath gives better results than any other.
"I will just make a few scratches on this fourth sheet of paper so. It leaves no mark. But it has the remarkable property of becoming red in vapour of sulpho-cyanide. Here is a long-necked flask of the gas, made by sulphuric acid acting on potassium sulphocyanide. Keep back, Dr. Waterworth, for it would be very dangerous for you to get even a whiff of this in your condition. Ah!
On the whole, the bath that has given the best results is one containing, in addition to gold, a small quantity of hypo and a considerable quantity of sulphocyanide of ammonium. Such a bath tones very rapidly, and gives most pleasing colors.
The sulphocyanide of potassium, KCsy, is prepared by fusing ferrocyanide of potassium, deprived of its water of crystallization, intimately mixed with half its weight of sulphur and 17 parts of carbonate of potassa.
A certain proportion of the ingredients namely, that of bath No. 3 gives better results than any other proportions tried, and about as good as any that could be hoped for. Any of the ordinary alkaline toning baths may be used, but they all give results inferior to those got by the sulphocyanide bath. The best of the ordinary baths is, however, the phosphate of soda.
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