SILVER ASSAYING 



829 



Table of Correction for the Variations in the Temperature of the Normal System 



of the Salt. 



The columns 5, 10, 20, 25, 35, have been calculated in the same manner for the 

 cases in which the normal solution may have been graduated to each of these tem- 

 peratures. Thus, to calculate the column 10, the number 100-118 has been taken in 

 the column of weights for a term of departure, and its difference from all the numbers 

 of the same column has been sought. 



Several expedients have been employed to facilitate and abridge the manipulations. 

 In the first place, the bottles for testing or assaying the specimens of silver should all 

 be of the same height and of the same diameter. They should be numbered at their 

 top, as well as on their stoppers, in the order 1, 2, 3, &c. They may be ranged suc- 

 cessively in tens ; the stoppers of the same series being placed on a support in their 

 proper order. Each two bottles should, in their turn, be placed in a japanned tin case 

 (Jig. 1848) with ten compartments, duly numbered. These compartments are cut out 

 anteriorly to about half their height, to allow the bottoms of the bottles to be seen. 

 When each bottle has received its portion of alloy, through a wide-beaked funnel, 

 there must be poured into it about 10 grammes of nitric acid, of specific gravity 1'28, 

 with a pipette, containing that quantity ; it is then exposed to the heat of a water- 

 bath, in order to facilitate the solution of the alloy. The water-bath is an oblong 

 vessel made of tin-plate, intended to receive the bottles. It has a moveable double 

 bottom, pierced with small holes for the purpose of preventing the bottles being bro- 

 ken, as it insulates them from the bottom, to which the heat is applied. The solution 

 is rapid ; and, since it emits nitrous vapours in abundance, it ought to be carried on 

 under a chimney. 



The Agitator. Fig. 1849 gives a sufficiently exact idea of it, and may dispense with 

 a lengthened description. It has ten cylindrical compartments, numbered from 1 to 

 10. The bottles, after the solution of the alloy, are arranged in it in the order of their 

 numbers. The agitator is then placed within reach of the pipette intended to measure 

 out the normal solution of salt, and a pipette full of this solution is put into each phial. 

 Each is then closed with its glass-stopper, previously dipped in pure water. They are 

 fixed in the cells of the agitator by springs. The agitator is then suspended to a, 

 spring K, and, seizing it with both hands, the operator gives an alternating rapid 

 movement, which agitates the solution, and makes it, in less than a minute, as limpid 

 as water. This movement is sometimes promoted by a .spiral spring, B, fixed- to the 



