"Water is readily detected, either in ether or alcohol by allowing a drop to fall into spirits of turpentine, with which they ought to mix without turbidity; this is immediately produced if they contain water: for detecting water in alcohol, benzole is a more delicate re-agent than spirits of turpentine (Chemist, xxix, 203). It is also necessary that ether should be free from a remarkable property it acquires by long keeping, of decomposing iodides and setting free iodine, which thus gives the collodion a brown color; the same property may be developed in any ether, as Schonbein discovered by introducing a red hot wire into the vapor in the upper portion of a bottle containing a little ether and water; if it be then shaken up and a solution of iodide poured in, the whole rapidly becomes brown; this reaction is very remarkable and difficult to explain for even a mixture of the ether and nitric acid fails to produce a color immediately. Ether thus affected can only be deprived of this property by rectification with caustic potash."
Bromo-Iodized Collodion for Positives.—No. 1.
IODIZED COLLODION FOR POSITIVES.
One very important object in connection with this part of the collodion process is to have chemicals of a good quality, and always employ those of a fixed standard.
| Plain collodion, | 10 | ounces. |
| Solution of bromide, and iodide of potassium and silver, ([page 61]) | 3 | drachms. |
| Iodide of ammonium, | 10 | grains. |
| Hydro-bromic acid | 6 | drops. |
Double iodide of potassium and silver (see [page 62]) enough so that when the plate comes from the nitrate of silver bath, it will have an opaque cream color.
Remarks.—In the preparation of this sensitive collodion, it is necessary to be cautious and not add too much of the iodide of potassium and silver, for in that case the coating would flake off, and falling into the silvering solution, the operator would be obliged to filter it before he could silver his plate with safety as regards spotting it.
The method I employ is to add the plain collodion, bromide and iodide of potassium and silver, iodide of ammonium and hydro-bromic acid, and then cautiously add the double iodide of potassium and silver from five to ten drops at a time, trying the collodion from time to time by pouring a little on a narrow strip of glass, which I dip into the silvering solution, and let it remain for two minutes. If the coating assumes the proper color (a cream color), I shake the contents of the bottle, and then stand it aside to settle: it is better after it has stood for a week or two.
This collodion I have used after it has been made eight months, and produced fine and satisfactory results, and use this nearly altogether in practice. Since the first edition of this work has been issued, I have sold over two thousand pounds of this preparation, and the demand is on the increase. I will append another preparation (No. 2) which I have successfully employed, and some operators prefer.