254 Transactions of the 



only just long enough to get an image so that a prolonged develop- 

 ment is required, the resulting print will be of a fine black colour ; 

 but if a very long exposure is given, and the development corre- 

 spondingly shortened, the print is softer and has the colour of a 

 lead-pencil drawing, which is better for microscopic objects. The 

 positive having been washed and toned, the next step is to apply to 

 its surface a piece of paper which has previously been coated with a 

 layer of gelatine, about gr. xxv. gelatine to 5 j of water, to which 

 about five drops of glycerine and a trace of chrome alum has been 

 added. The best way to effect this transference of the film is to 

 lay the plate in a dish of clean water, not necessarily distilled ; a 

 piece of the prepared paper is soaked in the water until thoroughly 

 wet and then applied to the face of the positive beneath the surface ; 

 the latter is then lifted out of the water with the paper on it ; this 

 prevents all air-bubbles getting between the two, but if any should 

 chance to find an entrance they must be gently pressed out. The 

 plate having been allowed to get dry, is again soaked in water for a 

 few hours, when the paper may be lifted off with the collodion film 

 attached. Very often the film will come off without previous drying, 

 but it is safer to do so ; if it comes off when it is dry, as it some- 

 times will, we have a print with a highly pohshed surface, which is 

 no doubt very pretty but not so good in an artistic point of view. 

 If the above directions should be faithfully followed, a print giving 

 all the details of the original negative, and magnified three diameters, 

 will be the result. I will conclude this paper with an account of a 

 mode of transferring negatives whereby they can be carried about by 

 dozens as easily as so many sheets of tissue-paper, and by which 

 means the glass plates can be used over and over again for an indefi- 

 nite length of time, until they get so much scratched as to be 

 worthless. They can be cleaned between each time of being used, 

 by a strong solution of washing-?oda ; they should be allowed to 

 soak in this for at least a week. The fluid which forms the tissue, 

 which I believe was first recommended by Mr. Walter Woodbury, 

 is made as follows : — 12 gr. of pyroxyhne is dissolved in each ounce 

 of a mixture of equal parts of ether and alcohol and 25 drops of 

 castor oil subsequently added; the proportions must be properly 

 arranged within certain limits ; if too much castor oil is added the 

 resulting film will be sticky and soft, if too little it will easily break. 

 To use this fluid it is necessary to prepare the negative beforehand, 

 by pouring over it, after it has been sufiiciently washed, a very weak 

 solution of gum, one part of ordinary office gum to five or six parts 

 of water ; this must be done twice. If too strong a solution is 

 applied the film will crack in all directions ; if not enough the 

 image will be dissolved. When the negative is dry it is carefully 

 placed in a horizontal position, Ijy means of a levelling stand, and 

 the liquid is poured over it ; this must be done with great circum- 



