Chemistry and Physics. 361 



yellow precipitate, invariably produced by traces of sodium 

 present, ceases to be formed after keeping the liquid for several 

 hours. The liquid is then filtered and the addition of caesium 

 nitrate continued until about 2-5 g. have been used. The reagent 

 is most sensitive when a precipitate of yellow, hexagonal plates, 

 a nitrite of caesium and bismuth, is formed on further addition of 

 the caesium salt. With 2 CC of this reagent 0-l cc of a 0*5 per 

 cent solution of sodium, as nitrate, gave a considerable precipitate 

 within 5 minutes, and by long standing it was found possible to 

 detect as little as 0*01 mg. of sodium in the presence of much 

 potassium salt. Most of the heavy metals interfere with this 

 test, but zinc, cadmium, magnesium, barium, calcium, strontium, 

 lithium, thallium and potassium do not interfere with it. The 

 formula for the precipitate appears to be 5Bi(N0 2 ) 3 .9CsN0 2 .- 

 6NaN0 2 . 



Preliminary experiments indicate that small amounts of sodium 

 may be quantitatively determined very accurately by means of 

 this method. The precipitate contains only 3*675 per cent of 

 sodium. — Jour. Chem. Soc, xcv, 2126. h. l. w. 



2. Volumetri'c Determination of Sulphates. — Mitchell and 

 Smith have worked out the details of a method for this purpose, 

 which is based on well-known reactions, and which had been sug- 

 gested, in its essential features, by Precht as early as 1879. They 

 take a convenient quantity of a sulphate, dissolve it in water or 

 pure hydrochloric acid, or, if necessary, dilute nitric acid, and 

 then add a slight excess of 1/5 normal barium chloride solution. 

 They then boil the mixture, make it neutral with ammonium 

 hydroxide, add ammonium acetate, acetic acid, and a slight 

 excess of 1/10 normal ammonium dichromate solution, make up 

 the mixture to 100 cc , allow the precipitate to settle, take out 25 cc 

 of the clear liquid and titrate it with 1/20 normal ferrous 

 ammonium sulphate, using potassium ferricyanide as an external 

 indicator, and taking the first tinge of green as the end point. 

 They use ammonium dichromate on account of the fact that 

 barium dichromate appears to carry down with it traces of the 

 potassium salt. The method was tested with ammonium sulphate, 

 sodium sulphate, potassium sulphate, zinc sulphate, magnesium 

 sulphate, and copper-ammonium sulphate. With potassium 

 sulphate there was evidence of adsorption, to the extent of nearly 

 2 per cent, but this was minimized by boiling the precipitate for 

 several hours with a little dilute hydrochloric acid, neutralizing 

 with ammonia, and proceeding as before. It is to be observed 

 in applying this method that ammonium dichromate which is 

 1/10 normal in regard to oxidizing power, is only 1/30 normal 

 in regard to precipitating power. The test analyses give very 

 satisfactory results, and it is stated that, excluding weighings, 

 five determinations can be made in an hour. — Jour. Chem. Soc, 

 xcv, 2198. h. l. w. 



3. The Action of Metals on Fused Caustic Soda. — As there 

 are conflicting statements in respect to the stability of sodium 



