88 Colorado College Studies. 



The recipes of chemistry are not like those of the cuisine; 

 the latter deal with a palate which is insensible between cer- 

 tain wide limits — the range embraced between the extremes 

 "too salt," and "not salt enough," being a fairly wide one, and 

 easily hit off. But the recipes of chemistry have to do with 

 indicators which are so fastidious that there is always either too 

 much or too little salt for their taste; and the object of indirect 

 or volumetric weighing, is to give them a little too much salt, 

 but at the same time to contrive that the excess is infinitesimal 

 in comparison with the degree of accuracy aimed at. 



If a known weight ly of silver nitrate be dissolved in a known 

 volume (a litre, say) of water, so that one drop of the solution 

 contains roW m. g. of dissolved silver salt, then it is clear that by 

 adding such a solution, drop by drop, from a burette to the com- 

 mon salt solution, a very much more accurate and quicker result 

 will be obtained than by the first procedure. If x c. c. of the 

 silver solution, as read off from the burette graduations, have 

 been used, then we know that 1 gramme of salt requires 

 exactly "^^^ grs. of silver nitrate to precipitate it, provided only 

 that the gradiudions of the hurefte used to measure both the 

 X c. c. and the litre are consistent among themselves. The 

 determination whether or no this is the case constitutes the 

 " calibration of the burette."* 



The method of calibration given in all text books is roughly 

 as follows. The burette is filled with water, and successive 

 portions, corresponding to 5 c. c. or so, are run out into dry 

 beakers. From the weights of these successive portions a table 

 of corrections can easily be deduced. This method in the case 

 of an ordinary 50 c. c. burette and with 5 c. c. tests, involves at 

 least 11 weighings and 10 level-readings. 



The method of calibration 1 would suggest is, I believe, 

 more accurate than the above, and involves no weighing what- 

 ever; for it is quite a matter of indifference to the chemist, 

 whose measurements are all relative, whether he adopts as his 

 uuit the true cubic centimetre, or an arbitrary one. 



