The iodized collodion is now poured on, and the excess returned to the bottle. Collodion can be made very easily, but if prepared without due precautions, it cannot be used afterwards, and reminds one of the old story of the enthusiastic son, who, when asking his father's permission to espouse the beloved, enumerated amongst her other accomplishments, the fact that she _could_ make a pudding, and was answered by the bluff question, "But can you eat it afterwards?" So it is with collodion: a great deal of messing and loss of time is saved by purchasing it of the various makers, amongst whom may be specially noticed Mr. Richard Thomas, of 10, Pall Mall, who has devoted the whole of his attention to the preparation of this important photographic chemical, and with a success which his numerous patrons can well testify. The collodion is sold either mixed with the iodizing solution, or the two can be obtained separately, with directions on the bottles as to the quantities to be mixed together. The plate covered with the iodized collodion is quickly transferred to a bath containing a solution prepared in the following manner:--Dissolve four ounces of nitrate of silver in eight ounces of water, and to this add twenty grains of iodide of potassium in one ounce of water; shake them together, and then pour the whole into fifty-six ounces of distilled water, and in half an hour add one ounce of alcohol and half an ounce of ether; agitate the whole and filter the next morning. The collodion plate is kept in this solution for a certain period, only learnt by experience, and should be occasionally lifted out to see if a uniform transparency is obtained; say that the immersion may be continued for five minutes, it is now ready for the camera, and may be exposed from about one to two minutes, or more if the light is deficient; the time of exposure is also a matter of _practice_, mere directions can be of no use in this stage of the process. The picture is developed on a levelled stand, with a solution of three [Page 148] grains of pyrogallic acid in three ounces of water, to which sixty drops of glacial acetic acid have been added. When fully developed the plate is washed with water and fixed with a solution of hyposulphite of soda, consisting of one part of the saturated solution to eight of water, again thoroughly but gently washed, so as not to endanger the separation of the film from the glass; it is allowed to dry spontaneously, and being coated with amber varnish (a solution of amber in chloroform) is now ready to print from. (Fig. 123.) It is, perhaps, hardly necessary to add, that the sensitizing and developing processes must be performed in a dark room. [Illustration: Fig. 142. A. Glass or gutta-percha bath to hold the sensitizing solution. B. Glass, with piece cemented on the end to hold the prepared glass plate, C, whilst dipped in the bath, A. The plate C has a cross in one corner to show prepared side.]