558 



SCIENCE 



[N. S. Vol. LIV. No. 1405. 



of one or two in the fifth decimal place and prob- 

 ably in the sixth place, and that a given bob as 

 modified will cover a range of about two decimal 

 places, that is, with one instrument, for example, 

 densities ranging from 1.00001 to 1.00010 could 

 be read. The modification consists in attaching 

 a light chain to the bob which is a fish-shaped, 

 hollow glass, or silica bulb. It is evident that if 

 the weight of such a bob (a certain amount of 

 ballast is usually necessary) is approximately that 

 of an equal volume of the liquid in which it is 

 placed, it will assume a position of equilibrium be- 

 tween the surface of the liquid and the bottom of 

 the containing vessel, the equilibrium being brought 

 about by the chain suspended from its lower end. 

 As the bob rises it lifts the chain link by link 

 off the bottom of the vessel till the added weight 

 counteracts the upward tendency and of course 

 the reverse takes place if the bob tends to sink. 

 A practical instrument utilizing this principle is 

 made by having the bob in a tube open at both 

 ends and with one end of the chain attached to the 

 lower end of the ''tube, so that it hangs in a loop 

 (catenary curve) between this point of support 

 and the bob. The density of a liquid in which 

 this instrument is placed can be determined by 

 noting the position which the bob takes with re- 

 spect to a scale on the tube. There are a number 

 of interesting variations of the instrument thai 

 can not be given in a brief abstract. 



The comparative value of different specimens of 

 iodine for chemical measurements: C. W. Foulk 

 AND Samuel Morris. Iodine was purified in va- 

 rious ways as described in the text-books of ana- 

 lytical chemistry and these preparations were 

 then compared through the medium of a sodium 

 thiosulphate solution with a specimen of iodine 

 that had been purified as if for an atomic weight 

 determination. Several new modifications of ap- 

 paratus for purifying and drying iodine were also 

 devised. The general conclusion drawn from the 

 experiments was that the so-called ' ' analytical ' ' 

 iodine is remarkably pure. Doubt, however, is 

 thrown on the use of a sulphuric acid desiccator as 

 a method of drying iodine when the water it con- 

 tains had been entrained through the solidification 

 of the iodine in the presence of liquid water. 



Variation of grain size in photographic emul- 

 sions in relation to photochemical and photo- 

 graphic properties: E. P. Wightman, A. P. H. 

 Trivelli and S. E. Sheppard. 



The physico-chemical properties of strong and 

 weak flours III. Viscosity as a measure of hy- 



dration capacity and the relation of the hydrogen- 

 ion concentration to imiihition in the different 

 acids: Eoss Aiken Gortner and Paul Francis 

 Sharp. In continuation of the work reported at 

 the Chicago meeting of the Society, the authors 

 have applied the use of the viseosimeter to the 

 study of hydration of the emulsoid colloids pres- 

 ent in wheat flour. Instead of using the washed 

 out gluten as in previous work a 20 per cent, sus- 

 pension of the entire flour was used in the present 

 study. The results indicate (1) that the viseosim- 

 eter affords an accurate and rapid means of 

 measuring imbibition, (2) the form of the vis- 

 cosity curves is identical with that of the im- 

 bibitional curves obtained previously by weighing 

 gluten discs, (3) "strong" flours give greater 

 viscosity values than do weak flours at the cor- 

 responding concentration of acid calculated on 

 either normality or hydrogen-ion concentration 

 basis, (4) when the viscosity is plotted against 

 hydrogen-ion concentration instead of against 

 normality of acid a radically different form of 

 curve results, with a maximum viscosity at about 

 Ph =: 3.00, (5) the same value for maximum 

 viscosity is not reached by all acids at the same 

 hydrogen-ion concentration, (6) the order of the 

 acids as influencing imbibition (lyotropic series) is 

 not the same for all of the flours studied. 



An interesting colloid gel: Eoss Aiken Gort- 

 ner AND Walter F. Hoffman. A rigid gel can 

 be prepared from di benzoyl 1. cystine containing 

 as little as 0.15 per cent, of the compound. 

 Viewed by dark field illumination this is ap- 

 parently a crystal gel. It is suggested that 

 this material may assist in studies regarding gel 

 structure for it can be easily prepared in pure 

 cystalline form and is consequently not affected 

 by previous history as is gelatin, agar, etc. 



Are electrolytes completely ionised at infinite 

 dilution? Harold A. Fales and Harold E. Eob- 

 eetson. Measurements made on hydrochloric, 

 acetic, sulphuric and phosphoric acids up to a 

 dilution of three million liters per mol, by the 

 electromotive force method using the ballistic gal- 

 vanometer, show that the thermodynamic ioniza- 

 tion passes through a minimum and approaches 

 zero with increasing dilution. It seems that it 

 is not until a dilution of one thousand liters per 

 mol is reached that the thermodynamic concen- 

 tration of hydrogen ion becomes equal to the 

 ionic concentration. 



Charles L. Parsons, 



Secretary 



