1884.] the Atomic Weight of Cerium. 155 



much silver was required to precipitate the chlorine of the cerium 

 chloride, assuming at the outset the atomic weight of cerium was 

 141 "0. I then weighed in a porcelain crucible that quantity, less 

 about 10 mgrms., and ignited it in a current of dry and purified 

 hydrogen, keeping it some time at a red heat, allowed it nearly to 

 cool in hydrogen, and then heated it again nearly to redness in air. 

 After cooling over sulphuric acid the silver was weighed and trans- 

 ferred to a 20-oz. bottle, and the empty crucible was again weighed. 

 A sufficient quantity of nitric acid, sp. gr. 1*42, was added to the 

 silver, and the stopper of the bottle, which had been previously 

 well ground in with emery, was tied down fast. The bottle was then 

 placed in a water-bath, and the water was heated gradually until it 

 boiled. It was kept at this temperature nearly an hour. There was 

 no escape of gas at the stopper; if the stopper ever did slip the 

 silver being dissolved was rejected, and a fresh quantity was weighed. 

 The solution of the silver was made some time before it was required, 

 so that the bottle and contents were quite cool when opened. After 

 carefully cleaning the neck and stopper of the bottle on the outside 

 the stopper was loosened and washed down into the bottle, a little 

 more water was added when the silver was found to be completely 

 dissolved, and the solution to be perfectly clear. The succeeding 

 operations were performed in a room from which daylight was 

 excluded. The solution of cerous chloride was poured into the 

 solution of silver nitrate in the bottle in which it was prepared, 

 and the whole was well shaken. The additional quantity of silver 

 required for the complete precipitation of the chlorine was added by 

 means of an approximately centinormal solution of silver nitrate, 

 1 grm. of which contained '001064 grm. of silver. As I did n6t 

 measure the quantity of the solution used but weighed it, I discarded 

 the "ordinary forms of burette in favour of a convenient sized' bulb 

 which I fused on to a glass stopcock ; in this shape it was more easily 

 weighed. The titration was made in an oblong box, divided into two 

 compartments by a partition. The inside of the box was well 

 blackened. In the partition a round hole was bored lj inch in 

 diameter ; in the right-hand compartment a lamp was placed, and 

 between it and the hole in the partition a spherical flask containing 

 a solution of potassium chromate, so that the light from the lamp 

 before passing through the hole had to pass through the yellow liquid 

 in the flask. In the left-hand compartment the bottle containing the 

 chloride was placed in such a position that the upper portion and 

 surface of the liquid it contained was illumined by the pencil of 

 yellow light proceeding through the hole. The burette was fixed in 

 a stand in the box, so that it dropped the solution of silver nitrate 

 into the bottle when the latter was in the best light. By this arrange- 

 ment the slightest turbidity produced in the liquid by the silver 



