PREPARATION 



KEA<;/<:NTS 



269 



like food, good even under quite diverse proportions and methods of prepara- 

 tion. With a few, however, it is necessary to have definite strengths. 



FIGS. 215-217. Graduates of various forms for measuring liquids. 

 (Cuts loaned by the Whitall To turn Co.] 



By a saturated solution is meant one in which the liquid has dissolved all 

 that it can of the substance added. This varies with the temperature. It is 

 well to have an excess of the substance present then the liquid will be satu- 

 rated at all temperatures usually found in the laboratory. 



\ 375. Solutions less than 10 per cent. In making solutions where dry 

 substance is added to a liquid if the percentage is not over 10%, the custom 

 is to take too cc. of the liquid and add to it the number of grams indicated by 

 the per cent. That is for a 5% solution one would take ico cc. of the liquid 

 and 5 grams of the dry substance. This does not make a strictly 5% solution. 

 For that one should take 95 cc. of liquid and 5 grams of the dry substance ; or 

 if the percentage must be exact then one should weigh out 95 grams of the 

 liquid and add 5 grams of the dry substance. 



Fi<;s. 218-219. Scales for weighing chemicals. (Cuts loaned by the Bausch 

 & Lomb Optical Company.) 



376. Solutions of 10 per cent and more. When the percentage is 10% or 



