once or twice, and the gun-cotton, if good, will entirely dissolve.  As soon as the silver is all dissolved, and while quite hot, pour out the above bromized collodion into a clean 4-ounce measure, having ready in it a clean slip of glass.  Pour into it the hot solution of silver in a continuous stream, stirring rapidly all the while with a glass rod.  The result will be a perfectly smooth emulsion without lumps or deposit, containing, with sufficient exactitude for all practical purposes, 8 grains of bromide, 16 grains of nitrate of silver, and 2 drops of hydrochloric acid per ounce.  Put this in your stock solution bottle, and keep it in a dark place for twenty-four hours.  When first put in, it will be milky; when taken out, it will be creamy; and it will be well to shake it once or twice in the twenty-four hours.

At the end of this time you can make your two dozen plates in about an hour.  Proceed as follows:  Have two porcelain dishes large enough to hold four or six of your plates; into one put sufficient clean water to nearly fill it, into the other put 30 ounces of clear, flat, not acid, bitter beer, in which you have dissolved 30 grains of pyrogallic acid.  Pour this through a filter into the dish, and avoid bubbles.  If allowed to stand an hour, any beer will be flat enough; if the beer be at all brisk, it will be difficult to avoid small bubbles on the plate.  At all events, let your preservative stand while you filter your emulsion.  This must be done through perfectly clean cotton-wool into a perfectly clean collodion bottle; give the emulsion a good shaking, and when all bubbles have subsided, pour it into the funnel, and it will go through in five minutes.  The filtered emulsion will be found to be a soft, smooth, creamy fluid, flowing easily and equally over the plates.  Coat with it six plates in succession, and place each, as you coat it, into the water.  By the time the sixth is in, the first will be ready to come out.  Take it out, see that all greasiness is gone, and place it in the preservative, going on till all the plates are so treated.

A very handy way of drying is to have a flat tin box of the usual hot plate description, which fill with hot water, then screw on the cap; on this flat tin box place the plates to dry, which they will do rapidly; when dry, store away in your plate box, and you will have a supply of really excellent dry collodion plates.

Just a word as to the preparation of the glasses before coating.  It is very generally considered that it is better the glasses receive either a substratum of albumen or very weak gelatine.  I use the latter on account of the great ease of its preparation.  After your glasses are well cleaned, place them in, and rub them with a weak solution of hydrochloric acid of the strength of 2 ounces acid to 18 ounces water.

Prepare a solution of gelatine 1 grain to the ounce of water, rinse the plate after removal from the acid mixtures, and coat twice with the above gelatine substratum; the first coating is to remove the surplus water, and should be rejected.  Rear the plates up to drain, and dry in a plate rack or against a wall, and be careful to prevent any dust adhering to the surface while wet.