bromic acid may sometimes be used witli advantage. The assay 

 pieces, having oeen carefully weighed, aiv plan-d in numbered 

 bottles, and a definite amount of moderately dilute nitric acid is 

 added to each, the bottles being then gently heated to assist 

 solution. The standard solution is then carefully introduced by 

 means of a pipette, and the bottles are vigorously shaken until 

 the precipitate coheres and the solution becomes clear. A cubic 

 centimetre of " decimal " solution, which is T Vth as strong as the 

 "' standard solution, is then added to each bottle, and they are 

 again shaken. This is repeated until the decimal solution 

 produces either no cloud or a very slight one. This indicates the 

 conclusion of the operation, as the amount of silver present can 

 be calculated when the weight of salt which is required to 

 saturate it is known. 



From the above description it will be seen that the only 

 special apparatus required in assaying silver by the method of 

 Gay Lussac is a pipette for measuring out the " standard " 

 solution, and one for adding " decimal " solution. 1 and 2 are 

 the forms of these used in the Royal Mint. The pipette for 

 standard solution, 1, is fixed in a vertical position and filled by 

 an indiarubber tube from below. The opening at the upper end 

 of the pipette is closed by the finger, the indiarubber tube is 

 removed, and the solution thus accurately measured is added to 

 the contents of a bottle. No. 2 is divided into cubic centimetres, 

 and the additions made by means of it as already described. 



7. Gay Lussac's apparatus for assaying silver by the 

 wet way. 



E. 98. 1885. 



Copper cistern lined with resinous cement to contain the 

 normal solution of salt, 100 standard measures of which corre- 

 spond with 896-thousandths of fine silver in the assay. Funnel 

 for use in filling the cistern. Pipette of 100 c.c., for use with 

 normal solution. Pipette for use with decimal salt solution, 

 Pipette for use with the decimal silver solution. Cage for 

 conveying the bottles to the shaking apparatus. Shaking 

 apparatus, filled with 10 assay bottles in position for use. Dark 

 case for bottle, containing the decimal silver solution. Case in 

 which the assay bottle is placed during the addition of tin- 

 normal solution to the assay. Hollow pillar, with sponge for 

 absorbing the excess of liquid from the front pipette during the 

 adjustment of the level to gauge mark. Water bath ns,-d for 

 heating assay bottles during the solution of assay pn-< 

 Bellows used for removing the nitrous fumes from the assay 

 bottles. Whisk used for stirring the salt solution in the cistern. 



8. Muffle containing cupels. 



1876. Lent by the Master of the Mint. 



