Put these into a quart bottle, and shake until the crystals are all dissolved, and this can be kept for a stock bottle, and when wanted for use pour into another bottle.
| Of the above solution, | 5 | ounces. |
| Acetic acid (No. 8) | 1 | " |
| Chemically pure nitric acid | 20 | drops. |
Shake this mixture well, and filter through a sponge, and it is ready for use. I file a mark in this bottle indicating five ounces, and another for 1 ounce: this will save time in mixing the solution.
Remarks.—In my recent tour of the United States, I found it difficult to obtain a good article of protosulphate of iron, and in its stead I used the common copperas, such as I could find almost in any store. I employ from one-fourth to one-half more than the quantity given above. If it looked a clear green, and free from a white or brownish powder, about one-fourth addition: i. e., four ounces, instead of three, as given above. If the solution in the stock bottle is not wanted for a week or more, a few crystals of the protosulphate of iron should be added, as it decomposes, and the strength is depreciated.
There is quite a difference in the strength of the acetic acid as sold by out country druggists, and the operator should be sure that he has No. 8, to which quality the above proportions are adapted. I never have employed the developing solution but once, but can see no objections to use it for a number of glass plates, but it should be filtered every time before using. The quantity of nitric acid may be increased, so long as a proper proportion is preserved with the strength of the bath. The effect of this addition of acid will be to brighten the impression; but if carried too far, the reduction (developing) will be irregular, and the harmony of the impression injured.
Fixing Solution.
FIXING SOLUTION.
| Water, | 8 | ounces. |
| Cyanide of potassium, | about 1 | drachms |
Remarks.—I put enough of the cyanide of potassium into the water to make the solution of such strength as to dissolve off the iodide of silver ("coating") in from twenty to sixty seconds. The operation is quite similar to that of hyposulphate of soda upon the coating of the Daguerreotype plate. A too concentrated solution is likely to injure the sharpness of the image.