Chemistry and Physics. 461 



that nitric acid, being monobasic, is incapable of forming acid 

 salts. Wells and Metzger have recently found that rubidium 

 and caesium each form two acid nitrates which are comparatively 

 stable, and they have also prepared an acid thallous nitrate. 

 Ditte had made the thallous salt and one of the rubidium salts, 

 but he did not use the proper method for obtaining them in a 

 pure condition, and consequently did not ascertain their true 

 compositions. The recent additions and revisions give the fol- 

 lowing list of acid nitrates : 



KN0 3 -2HN0 3 

 NH 4 NO. -2HN0 3 NH 4 N0 3 HN0 3 



RbNO/2HN0 3 RbN0 3 HN0 3 



CsN0 3 -2HN0 3 CsN0 3 HN0 3 



T1NO.-2HNO, 



The caesium and rubidium salts form large colorless crystals 

 which, although somewhat unstable, may be readily handled at 

 ordinary temperatures ; in fact, CsN0 3 'HN0 3 is so stable that 

 it shows a sharp melting-point at 100°. The potassium, ammo- 

 nium and thallium acid nitrates have low melting-points, varying 

 from —3 to 18°, so that they require low temperatures for their 

 formation. The diacid salts are produced by dissolving the 

 normal nitrates in nitric acid of 1*50 sp. gr. and cooling to crys- 

 tallization, while the monacid salts are similarly prepared from 

 acid of 1-42 sp. gr. — Amer. Chem. Jour., xxvi, 271. h. l. w. 



4. Methods of Standardizing Acid Solutions. — Cyril G. 

 Hopkins has compared six different methods of standardizing 

 volumetric acid solutions. He finds that the determination of 

 chlorine in hydrochloric acid by weighing silver chloride in a 

 Gooch crucible gives more closely agreeing results than the other 

 methods that he has tried, while neutralizing sulphuric acid with 

 ammonia, evaporizing to dryness, heating the residual ammonium 

 sulphate to 120°, and weighing it (Wenig's method) also gives 

 very satisfactory agreements. The method of Hart and Croas- 

 dale, which consists in eleetrolyzing copper sulphate, weighing 

 the precipitated copper, and using the liberated sulphuric acid as 

 the basis, gave rather poorly agreeing results. Hartly's method 

 of standardizing with metallic sodium was found to be unreliable, 

 apparently on account of impurities in the sodium. Rimbach's 

 method, by use of crystallized borax with methyl-orange as an 

 indicator, was found to be unsatisfactory, because the borax 

 gradually lost water of crystallization in the air. This is con- 

 trary to Rimbach's experience, and is probably due to a differ- 

 ence in atmospheric conditions. The method of standardizing 

 oxalic acid by means of potassium permanganate solution, the 

 latter being compared with metallic iron, is stated to give fairly 

 good results. It would be interesting if the author had included 

 several other methods in his comparison ; for instance, Grogger's 

 method, which is based on the liberation of iodine by the action 

 of an acid upon potassium iodate and iodide, and also the very 



