Wet Collodion Process
The Metric System. Official Tables.
Those who wish to obtain full and authoritative tables of the metric system and its terms, as now legalised in the United Kingdom, should obtain "Statutory Rules and Orders, No. 411 of 1898." The price is one halfpenny, and it can be had from Eyre and Spottiswoode, East Harding Street, Fleet Street, E.C., and 32, Abingdon Street, Westminster S.W.; or John Menzies & Co., 12, Hanover Street, Edinburgh, and 90, West Nile Street, Glasgow; or Hodges, Figgis, & Co., Limited, 104, Grafton Street, Dublin.
Wet Collodion Process. Either negatives or positives can be produced ; and the latter, when taken upon thin enamelled-iron plates, are known as ferrotypes or tintypes. The following is a short resmne of the process: - A well-cleaned glass plate is coated with iodised collodion, and as soon as the collodion has, set, this coated plate is immersed in a bath made as follows: -
Nitrate of silver ...... ... ... 240 grs.
Potassium iodide ... ... ... ... 1 gr.
Distilled water ... ... ... ... 8 ozs.
Dissolve the silver salt in 2 oz. of water, and the potash in £ oz. Add the latter to the former, and add the remainder of the water. Filter, and test for acidity. If the blue litmus paper is not turned red after an immersion of some short period, a few drops of a dilute nitric acid (1 in 12) should be added till the bath is decidedly acid. The plate is exposed whilst still wet, the exposure being about ten times that for gelatine dry plates of ordinary rapidity under similar circumstances. For development any of the following may be used, but the author prefers Nos. 2, 3, and 4, the last being especially useful, as shorter exposure is required, and more detail is brought out. With No. 5 longer exposure is required, but extreme contrast is obtained : -
Ferrous sulphate ............ 300 grs.
Glacial acetic acid ... ...... ... 200 mins.
Methylated spirit ...... ...... oz.
Distilled water ............ 10 ozs.