The Collodion. Collodion is a mixture of alcohol, ether, py-roxvlin or gun - cotton, and sundry iodides and bromides, which are sometimess called "salts". When of proper consistency it is of the thickness of cream, and of a rich straw color. Spread upon the photographic plate,it serves to retain the sensitizing agent while subjected to the light, and to unite with it in forming the film from which the photographic image is developed. It is made as follows:

Ether........................

10 ounces.

Alcohol...............................

10 "

Iodide of Ammonium....................

60 grains.

Bromide of Potassium........................

20 "

0. In hot weather cadmium-hromide may be used in place of potas-129. The following modification is good:

Ether.....................................

6 ounces.

Some Brains.............................

Alcohol..........................

6 ,,

Some more Brains,................

Cotton,......................................

72 grains.

Some Iodide, and a little more Brains,.....................

Some Bromides, and a large quantity of Brains................

After the above is all dissolved and settled, add enough brains to make a good negative. - Hugh O'Neil.

Having made a number of trials with a view of determining what is the best strength for salting the collodion, and what the best for the bath, I have arrived at the conclusion that an increase in the sensitiveness is obtained when the collodion contains thirteen grains of iodides and bromides, and the bath is reduced to twenty - eight grains per ounce. - Elbert Anderson.