MAKING BLUE PRINTS 511 



and drying (and preserving) the paper should be carried 

 out in the dark room by the ruby light. The paper should 

 not dry too slowly. 



The two stock solutions will keep indefinitely, but should 

 be mixed only immediately before use as they soon spoil 

 after mixing. 



Any fine grained white paper may thus be sensitized. 

 For all routine work in the laboratory, however, it is advis- 

 able to buy ready prepared blue-print paper. This should 

 be of the finest quality as the success or failure of the whole 

 work depends on the quality of the paper. It can be bought 

 in rolls about 30 to 36 inches in widtli and of practically 

 any desired length (from F. Weber & Co., Philadelphia,, 



Fig. 390. Frame for making blue prints. This frame is 18 inches long by 8 inches- 

 wide. It is often advisable to use considerably larger frames if many blue prints are to 

 be made. 



St. Louis, and Baltimore). It should be thoroughly pro- 

 tected from the light and should be fresh when used. The 

 paper bought should be a light weight variety suitable for 

 printing in sunlight. 



The most important use for blue-print paper in the lab- 

 oratory is for the making of multiple copies of the kymo- 

 graph records obtained by students. For this work a large 

 printing frame (several of these should be provided) as 

 shown in Fig. 390 is used. These frames are about 8 



