82 abstracts: chemistry 



By substitution in the Clausius-Clapeyron equation of the data of 

 Vicentini and Omodei on the volume-change at the melting-point, and 

 of Person on the latent heat of fusion, dt/dp was calculated for each of 

 the four metals. The calculated values are in satisfactory agreement 

 with those observed. Incidentally, a convenient standard curve for 

 the calibration of copper constantan thermo-elements at temperatures 

 from to 425° has also been computed and included in the paper. 



L. J. and L. H. A. 



CHEMISTRY. — The phenomenon of occlusion in precipitates of barium 

 sidphate and its relation to the exact determination of sulphate. John 

 Johnston and L. H. Adams. Journal American Chemical Society, 

 33: 829. 1911. 



The occlusion by barium sulphate of other sulphates is a general 

 phenomenon. The amount of this occlusion depends upon (a) the com- 

 position of the original solution; (b) the fineness of the precipitate, which 

 in turn is conditioned by the degree of solubility of barium sulphate in 

 the particular medium, the rate of precipitation, and the time and man- 

 ner of standing between precipitation and filtration. The phenomenon 

 is therefore in all probability an absorption at the surface of the grains 

 of the precipitate, since it is affected by the factors just mentioned. 



On the basis of the knowledge gained in this way, attempts were made 

 to find a direct method for the determination of sulphate which should be 

 generally applicable, exact, and require only small and easily determined 

 corrections. The following procedure is suggested: To the solution 

 (300 cc. for a precipitate to weigh 2 grams) add 50 cc. of concentrated 

 hydrochloric acid, heat to boiling, and precipitate, stirring constantly, 

 with a 10 per cent solution of barium chloride. This should be added 

 at such a rate that about four minutes is required in running in the 22 

 cc. necessary; the rate is best regulated by attaching a suitable capillary 

 tip to the burette containing the barium chloride solution. Evaporate 

 the whole to dryness on the steam-bath (this may be done immediately 

 after precipitation), take up with hot water, filter thru paper, wash 

 until the washings are free from chloride, ignite very carefully (so as to 

 obviate reduction), and heat to constant weight over a Bunsen burner. 

 The necessary correction is determined by a concurrent calibration of 

 the method; that is, by dissolving an equivalent weighed amount of 

 pure dry sodium (or potassium) sulphate in a medium such that the 

 resulting solution is as nearly as may be of the same composition as the 

 solution to be analyzed; the sulphate in this comparison solution is then 



