80 On a Photographic Process. 



twee, when the trace of the dots of light appear as black 

 lines more or less, or as a blackened sm'face in the case of 

 Barograph. It only now remains to dissolve out the 

 unchanged Iodide of Silver by Hyposulphate of Soda, and 

 thoroughly free the papers from every trace of the latter salt 

 by washing, and the registers are complete. 



In this process many precautions are requisite ; in the dif- 

 ferent stages of preparing the paper they are the same as must 

 always be observed in photography ; and the development 

 especially requires great care. To secure good evenly waxed 

 papers in the first place was found with us to be no easy 

 matter, and required considerable time and fi-equent hot 

 pressings, care being taken that the temperature was not 

 higher than 212°. With every precaution, however, dark or 

 spotted papers frequently resulted with us, and we seldom 

 got a paper that, after fixing, returned any of its pristine 

 whiteness on the unaffected parts. 



Frequent comparative failures of this kind led me to ex- 

 periment, especially to obtain similar conditions of paper by 

 other materials than wax, and I found by far the best 

 result was got by using paraffin. The process was easier 

 and quicker, the papers were cleaner and of a better colour, 

 and best of alJ, the time occupied in the various processes of 

 sensitizing, developing, &c., was very much shortened. 



Paraffin has a lower melting point than wax, consequently 

 it can be kept fluid more easily, it permeates the paper much 

 quicker and more evenly, and one or two pressings in the hot 

 press are sufficient to get rid of all superfluous paraffin, and 

 render the whole batch nicely and evenly translucent. Both 

 ■ — waxing and paraffining papers — are done by having a tin 

 tray (large enough to hold a full sheet of photo-paper) fitted 

 on to a large water-bath ; in this tray the wax or paraffin is 

 melted and the papers dipped. A pile of paper is then made 

 up by placing one waxed or paraffined between six or seven 

 plain, and in the hot press the whole becomes evenly 

 saturated. 



Paraffin has the advantage over wax on many other points : 

 it is less sticky, the papers can therefore be separated more 

 easily after coming from the press, and very few are torn ; 

 they are also less greasy, and take the baths more quickly 

 and evenly, and when prepared are decidedly more sensitive. 



A few modifications in the preparation were suggested. 

 By experience it was found better to use a larger quantity of 

 free iodine in iodizing the papers, and not quite so strong a 



