CAMERA AND PHOTOGRAPHIC APPLIANCES 37 



They are furnished in two degrees of sensi- 

 tiveness and cover all demands, from the low- 

 est powers to the highest, equally well. 



All plates used in photo-micrographic work 

 should be backed. In fact the advantage of 

 so doing is even more marked than in other 

 branches of photography, where it is now 

 considered indispensable. Here again our 

 foreign cousins are better served than we. All 

 English plate makers furnish them ready 

 backed without extra cost. I believe but 

 cannot state positively that Carbutt is the 

 only American manufacturer who lists them, 

 but at an increased cost, and the backing, 

 though efficient, is so difficult to remove, and 

 makes such a mess of the developer that the 

 remedy becomes almost as bad as the disease. 

 As a consequence each one of us must learn 

 to back his own plates. A method of doing 

 this, published in one of the annuals some 

 years ago, is so simple, easy of application and 

 perfect in results, that I take pleasure in 

 reproducing it : 



Put 10 ounces of 95 per cent alcohol into a wide-mouth 

 bottle with % ounce of powdered white castilc soap, for a 

 stock solution. Shake the bottle occasionally until the 

 soap is dissolved, which may take a week or longer. When 

 half dissolved it is ready for use. Pour off 2 ounces and 

 filter, to which add 10 grains each of Erythrosin and Aurin, 



