NATURAL PHILOSOPHY. 181 



coating of gold. 6. Nitric acid is now applied, as in the common etching pro- 

 cess. The acid attacks the lines of the picture formed by the bare metal, but 

 will not bite into the gilded surface. A perfect etching is thus obtained. 



THE AMBROTYPE. 



This term has been applied to the result of a new process, recently patented 

 by James A. Cutting, of Boston, which consists in taking pictures photograph- 

 ically on a film of collodion, on the surface of a sheet of glass, the collodion 

 being suitably prepared for the purpose. The nature of the process will be 

 easily perceived by the following abstract of the specification accompanying 

 the patent : 



It has been found that when gun-cotton has been exposed to the action of 

 the atmosphere for the purpose of drying it, the sensitiveness of the collodion 

 prepared from it is sensibly diminished. By the use of alcohol it may be de- 

 prived of its moisture after being washed, without exposure to the air, and 

 without the constant deterioration of its sensitiveness. This part of my pro- 

 cess I conduct as follows: So soon as the cotton has been sufficiently exposed 

 to the acids, and has been thoroughly washed, it is plunged into strong alco- 

 hol, which effectually deprives it of the water which it contains, without 

 exposing it to the atmosphere for the purpose. From this alcohol it is taken 

 immediately to the mixture in which it is to be dissolved for the purpose of 

 forming the collodion. This mixture consists of 10 parts of sulphuric ether 

 and 6 of alcohol, or thereabouts. The collodion thus formed is allowed to 

 remain until it has settled perfectly clear, which usually requires about 24 

 hours. It is then decanted, and in every pint is added 80 grains of iodide 

 of potassium dissolved in alcohol. It is then well shaken, and 32 grains of 

 refined gum-camphor is added to each pint of the collodion, and after it is 

 again settled it is fit for use. The object of the camphor is to increase the 

 vigor and distinctiveness of delineation of the positive pictures, and particu- 

 larly of the half tints. It also greatly increases the beauty of the picture, by 

 giving a fineness of deposit not heretofore attained by any other means. The 

 use of the gum-camphor in the manner above described forms the second 

 branch of my invention. The collodion is then applied to the surface of the 

 glass in the following manner : 



The plate of glass being held horizontally, a portion of the collodion is 

 poured upon it, and it is then inclined in different directions, so as to cause 

 the collodion to flow over its whole surface, upon which it forms a colorless 

 transparent film ; the excess of collodion is then allowed to run off, and the 

 glass, being still held horizontally, is inclined to one side and the other, until 

 the collodion becomes partially thickened or set. "When this has taken place, 

 and before it is dry, it is rinsed in a solution of crystallized nitrate of silver, of 

 a strength of 40 grains to the ounce of water ; the film is thus impregnated 

 with iodide of silver, and after remaining in this bath a sufficient length of 

 time for the ether to escape from the collodion, the plate is ready to be placed 

 in the camera. After being exposed a sufficient length of time in the camera, 

 it is taken to a dark room, where the latent picture is developed by the appli- 



