August 10, 1917] 



SCIENCE 



143 



For the sugar solutions having concentra- 

 tions less than 25 per cent, the results do not 

 differ from the results for distilled water more 

 than is explainable by the accidental variation 

 normal to the method when the temperature is 

 not controlled precisely. The effects of one 

 hundredth normal acid and alkali found by 

 MacDougal were many times the variations 

 here observed and one may conclude that 

 neither sucrose nor dextrose, in concentrations 

 under 25 per cent., has any important effect 

 on the swelling of gelatine-agar gels in water ; 

 important, that is, in comparison with the 

 effects of acids or alkalis. With sugar con- 

 centrations of 50 per cent, the data show a 

 markedly lessened swelling of all the gels in 

 sucrose and of the two low-gelatine gels in 

 dextrose. It may be that the two high-gelatine 

 gels also swell less in 50 per cent, dextrose but 

 the decrease is not certainly determinable 

 from the single test which was made. This 

 decrease in swelling in concentrated sugar 

 solutions is to be expected from analogy with 

 the osmotic behavior of such solutions and 

 does not indicate any specific effect of either 

 sugar on the swelling or imbibition capacity 

 of the gels themselves. 



E. E. Free 



Desert Botanical Laboeatort 



THE AMERICAN CHEMICAL SOCIETY 

 III 



DIVISION OP INDUSTRIAL CHEMISTS AND CHEMICAL 

 ENGINEERS 



H. E. Howe, Chairman 

 S. H. Salisbury, Jr., Secretary 



A new method of separating sine from cadmium 

 and the latter 's determination iodometrically : 

 Eric John Ericson. The separation consists in 

 crystallizmg the zinc out as zinc sulphate or zinc 

 ammonium sulphate. It may be applied to the de- 

 termination of cadmium in ore or in spelter (after 

 removing and determining lead). In the latter 

 case, although a small trace of cadmium is en- 

 trained in the crystals, only one crystallization is 

 deemed necessary in view of the large sample 

 taken. After removal of zinc, the cadmium may be 

 determined by any of the usual methods. An 

 iodometric method is outlined. 



The determination of cadmium in brass: E. 

 Schramm. Owing to the lack of any well-tried 



method for the determination of cadmium in brass, 

 a series of analyses was carried out on brasses and 

 on mixtures of salts with and without additions of 

 cadmium. A procedure was developed which gives 

 fairly reliable results for the small amounts of 

 cadmium concerned. The method consists essen- 

 tially in removal of the copper electrolytieally from 

 nitric acid solution, followed by separation of the 

 cadmium from zinc with hydrogen sulphide, in so- 

 lutions of regulated acidity and small volume. 

 The cadmium is finally weighed as sulphate. 



The electrometric titration of zinc: F. Russell 

 V. BicHOwsKT. In the potassium ferrocyanide 

 method for determining zinc there are three prin- 

 cipal sources of error: (1) Oxidation of the ferro- 

 cyanide by any nitric acid, chlorine, or bromine 

 present; (2) precipitation of other metals along 

 with zinc; (3) uncertainty of the end point. To 

 remove the first source of error precautions such as 

 the addition of SO, should be taken. To avoid the 

 precipitation of other metals the rational proced- 

 ure is to change the conditions of the ferrocyanide 

 precipitation by carrying it out in solutions con- 

 taining from 10 to 20 per cent. HCl. In these solu- 

 tions zinc ferrocyanide is only slightly soluble, but 

 lead, manganese, iron and copper ferrocyanides 

 are very soluble. Since the ordinary indicators can 

 not be used at this concentration of acid, an elec- 

 trometric determination of the end point is 

 adopted, which is found to be quicker and more 

 accurate than the older methods. This consists in 

 noting the point at which there is a sharp change 

 in potential of the solutions against a platinmn 

 electrode. The apparatus is the same as that used 

 in determining the end-point of oxidation and re- 

 duction reactions in the analysis of iron, vanadium, 

 chromium, etc. Experiments on a number of salt 

 mixtures show that the end point is not affected 

 by the amount of acid or neutral salts present 

 within reasonable limits, nor by the presence of 

 iron, lead, manganese (up to 50 mg.), or by small 

 amounts of copper and cadmium. The preliminary 

 operations for the purification of the ore therefore 

 lose their customary importance; comparative re- 

 sults show that the electrometric method is more 

 rapid than the usual procedure. 



The vapor pressure of zinc and related metals: 

 John Johnston. A review of the somewhat scat- 

 tered observations on the vapor pressure of high- • 

 boiling metals, and a reduction of the data yield- 

 ing equations by means of which the vapor pressure 

 at any temperature can be ascertained. Published 

 observations on the volatility of metals, alone and 

 from mixtures, are also summarized. 



