CRITICAL EXPERIMENTS FOR DETERMINATION OF POTASSIUM, ETC. 579 



kept at 100° to 105° by means of a small chamber made of asbestos paste- 

 board, which enclosed it ; and the first step in each analysis was to make this 

 joint anhydrous by passing a current of chloride of calcium dry air through the 

 (heated) tube, until the chloride of calcium tube attached to its end ceased 

 to gain weight, taking care to have the silver spiral at a red heat during an 

 earlier stage of this preliminary operation. The expulsion of the water of the 

 substance was effected in a slow current of chloride of calcium dry air. 



The direct determination of the oxy chloride-oxygen is a far more difficult 

 problem, which we did not succeed in solving. To keep other chemists from 

 wasting their time, we will shortly sketch out the two methods which we tried. 



First Method. — A known weight of the chloroplatinate (contained in a 

 boat standing within a combustion-tube, which has a spiral of red-hot sheet 

 silver near its exit end) is heated to redness in a current of carbonic oxide, 

 with the view of determining the water as such, and any surplus oxygen as 

 carbonic acid. The former is collected in chloride of calcium, the latter in an 

 evacuated flask containing a measured volume of standard baryta-water to be 

 determined titrimetrically in the way which one of us employed successfully in 

 the analysis of sea- water (see "Challenger Memoir"; also Dittmar's Exer- 

 cises in Quantitative Analysis, section on Sea-water Analysis, pages 227-230). 

 To test the method, we applied it to a known weight of pure fused chloride of 

 silver. The carbonic oxide was prepared from oxalic acid, and kept in a Pisani 

 gas-holder over strongly alkaline pyrogallate of soda. Certain other precau- 

 tions which were taken are too obvious to be stated ; suffice it to say that we 

 obtained 16 mgs. of carbonic acid from a substance containing no oxygen* 



Second Method. — A known weight of the substance is heated in a current of 

 pure hydrogen to obtain all the oxygen (present as water, or in other forms) as 

 water, which is collected in a U-tube charged with pumice and oil of vitriol. 

 By avoiding all cork-joints we had no difficulty in collecting our water in that 

 U-tube, without any hydrochloric acid condensing along with it. To obtain 

 air-free hydrogen, we employed a Kipp apparatus, charged with zinc and boiled 

 out dilute sulphuric acid, and so communicating with a supplementary " Kipp," 

 discharging hydrogen, as to maintain an atmosphere of hydrogen in the upjDer 

 bulb of the other. The gas obtained was passed through a series of U-tubes 

 charged with sulphuric acid and pumice, and from the last U-tube direct into 

 a combustion-tube containing red-hot copper-gauze (and drawn out at both 

 ends to avoid cork joints), and thence again through a U-tube containing 

 sulphuric acid and pumice ; from this last tube the gas entered the combustion- 

 tube to do duty. This method, like the first, was rehearsed with pure chloride 

 of silver, and the result was that the chloride of silver yielded a very 



No doubt some COCl 2 had been produced from the CO and AgCl, and not all been decomposed by 



the silver spiral, although we operated at the highest temperature permissible in a Bohemian glass tube. 



