W. Crookes on the Wax-paper Photographic Process. 175 



sion. When practicable it is a good plan to allow water from a 

 tap to flow over the sheets for a minute or two, and having thus 

 got rid of the hyposulphite of soda from the surface, to allow 

 them to soak for about ten minutes in a large dish of hot water. 



54. They are then to be dried by hanging up by a crooked 

 pin, as after iodizing. When dry, they will present a very 

 rough and granular appearance in the transparent parts ; this is 

 removed by melting the wax, either before a fire, or, what is far 

 better, by placing them between blotting paper, and passing a 

 warm iron over them; by this means, the white parts will re- 

 cover their original transparency. 



55. The picture, arrived at this stage, may be considered fin- 

 ished, as far as is requisite for the purposes of measurement and 

 registration; sometimes, however, it may be necessary to multi- 

 ply copies, for the purpose of transmitting to other Meteorologi- 

 cal Observatories facsimiles of the records, or at least of those 

 containing any remarkable phenomena. I will therefore now 

 detail the method of .printing photographic positives from these 

 negatives, premising that the process does not differ materially 

 from that usually adopted. 



56. The only extra piece of apparatus required, is a pressure 

 frame; which consists essentially of a stout piece of plate glass 

 in a frame, with an arrangement for screwing a flat board, the 

 size of the glass, tight against it. Though apparently very sim- 

 ple, some care is required, when the frame is a large one, in 

 arranging the screw and board at the back, so as to obtain an 

 equal pressure all over the surface ; unless this is done, the glass 

 will be very liable to break. The pressure frames supplied to 

 us by Messrs Newman and Murray, 122, Eegent Street, are un- 

 exceptionable in this respect. The board should of course be 

 well padded with velvet, and the lateral dimensions of the glass 

 should be the same as those of the gutta percha dishes (8). 



57. The extra chemicals required for this process, are chlorid 

 of sodium, and chlorid of gold. Generally speaking, for the 

 former, common table salt will be found quite pure enough ; but 

 as the quantity required is but small, it will perhaps be found 

 better to obtain some of the recrystallized salt along with the 

 other chemicals. 



The chlorid of gold is merely required for an artistic effect. 

 Many persons object to the reddish brown appearance of ordi- 

 nary photographic positives ; the addition of a little chlorid of 

 gold to the fixing bath converts this into a rich brown or black ; 

 the trifling quantity required removes any objection to its use on 

 the score of expense. 



58. I prefer using the same kind of paper for positives as 

 for negatives (20). Messrs Canson manufacture a thicker paper, 

 which is generally called positive paper, but I think the thin is 



