THE CALIBRATION OF BURETTES. 



BY DOUGLAS CARNEGIE. 



The balance is the supreme tribunal of the chemist. No 

 matter how simple and brief, or how complicated and pro- 

 longed, a chemical operation may be, its alpha and omega is a 

 weighing. 



Oftentimes, however, the conditions of the investigation are 

 such that direct weighing cannot be carried out with the 

 exactitude demanded. In such cases, recourse is had to a 

 method of indirect weighing which I venture to call volumetric 

 ■weighing. 



It is the object of this note to show how this volumetric 

 weighing may be carried out with accuracy. 



Suppose that we wish to ascertain the exact quantity of sil- 

 ver nitrate that is necessary to completely precipitate 1 gramme 

 of common salt in a solution colored yellow by potassium chro- 

 mate. It is well known that if we^dd the silver nitrate in small 

 quantities to such a solution, the latter will finally change from 

 yellow to red, when just a little more silver nitrate has been 

 added than is necessary to precipitate the whole of the salt. 

 Suppose that in this investigation we add the silver nitrate in 

 small pinches from a quantity originally weighed, and that as 

 soon as the color change appears we weigh the quantity of sil- 

 ver salt remaining. It is obvious from what precedes that the 

 quantity of silver nitrate thus deduced will be two great by a 

 pinch, or some fraction of a pinch. If the average weight of 

 the pinches was, say, 1 m. g, : and the whole experiment turns 

 on i^J^th of this quantity, it is clear that the investigation does 

 not lend itself to a method involving direct weighings. 



