712 



SCIENCE 



[N. S. Vol. XXXVIII. No. 985 



ponent has had very little application in analytical 

 chemistry. The solubility curve of the system 

 ethyl alcohol-kerosene has been determined and the 

 curve, showing the variation of the maximum with 

 small additions of water, plotted. The change for 

 1 per cent, is 17.05°, but the variation is not quite 

 linear. With careful manipulation the critical 

 solution temperature can be determined repeatedly 

 to 0.01° and so may be used to indicate a change 

 of less than 0.001 per cent, in the water content of 

 the alcohol. If the moisture in the substance to 

 be examined can be transferred to anhydrous ethyl 

 alcohol by some suitable means, a very delicate 

 quantitative method is at hand. Since ethyl alco- 

 hol forms a mixture of minimum boiling point 

 containing about 5.5 per cent, water, all alcohols, 

 containing less than this amount of water, will 

 tend to distil off between 78.0° and 78.3°. Dis- 

 tillation of the moist substance with anhydrous 

 alcohol would be effective for the transfer of the 

 moisture. Standing with the alcohol at room or 

 higher temperatures might answer with certain 

 substances. The method has been used in moisture 

 determination in coal, wool, cotton, starch, sugar 

 and offers possibilities in the examination of food 

 products, soap, gelatin, shellac, oila, various tex- 

 tiles, etc. 

 George A. Perley and G-. F, Lane: The Analysis 



of Basic Lead Sulphates. 

 Edgar T. Wherry: Variations in the Compositions 



of Minerals. 



The old definition of a mineral species as a defi- 

 nite chemical compound is, in the light of recent 

 work, no longer tenable. Instead it should be: a 

 natural substance whose chemical and physical 

 properties are constant within certain limits which 

 vary considerably from one ease to another. Col- 

 loid minerals may vary by reason of adsorption; 

 meta-coUoids (colloids which have become crystal- 

 loidal) and crystalline ones by isomorphous re- 

 placement, solid solution and sub-mieroseopie inter- 

 growth. The group of ferric phosphate minerals is 

 discussed as an illustration. 

 Payson Bartlett: The Increase in the Oxidizing 



Potential of Dichromate Ion on Platinum Caused 



hy Certain Seducing Agents. An Improved 



Method for the Electrometric Titration of 



Ferrous Salts. 



Certain reducing agents increase the oxidizing 

 potential of the dichromate ion on platinum by 

 amounts up to two tenths of a volt. No other 

 oxidizing agent was found which would give a 

 similar effect. 



The potential continues to increase up to the 



very endpoint of the reaction and is highest when 

 the dichromate concentration is least. A final 

 drop of 0.1 normal reducing agent often depresses 

 the potential by half a volt. 



The duration of the effect varies with the re- 

 ducing agent used from a few seconds to many 

 hours. Chlorides are fatal to the permanency owing 

 apparently to a side reaction. 



The phenomenon may be plausibly explained by 

 assumptions of catalytic action. 



An improved apparatus and method for titrating 

 dichromate and ferrous salts, based on the phe- 

 nomenon, is suggested. 



When the endpoint of this reaction is determined 

 with a ferricyanide indicator, 0.0003 gram excess 

 of ferrous iron in each hundred cubic centimeters 

 of solution is present when the blue color barely 

 develops within thirty seconds. 



W. S. Hubbard: Equilibrium between Pyridine, 



Silver Nitrate and Water. 



While working on a silver-plating bath where 

 pyridine was used instead of cyanide, it was noticed 

 that under certain conditions of concentration and 

 temperature long silky, needle-shaped crystals 

 separated out. Brewer^ found that there were 

 three well-defined compounds formed with pure 

 pryidine and silver nitrate, but their description 

 in no way resembles the one found in this case. 



With 3 c.e. pyridine, 5 gm. silver nitrate and 

 made up to 100 c.c. with water, the crystals form 

 at 19.70° C. Using 4 c.c. of pyridine, they form 

 at 25.35°, with 5 e.c. they separate at 27.35° and 

 with 6 CO. pyridine at 27.75°. 



The exact composition has not been determined, 

 but the method will be to determine the total nitro- 

 gen and nitrate nitrogen and then determine the 

 silver electrolytically. The water can then be deter- 

 mined by difference or by drying in a desiccator 

 since it thus loses its water of crystallization and 

 becomes a fine powder. However, some of the 

 pyridine might thus be lost. 

 Philip Adolph Kober: New Precipitants for 



Copper, 



Two new precipitants for copper are proposed 

 which form very insoluble compounds of copper 

 (less than .6 part in one million remain unpre- 

 cipitated). These are amino acids, phenylglycin 

 and normal amino caproic acid which may be 

 useful in estimating Fehling's and other solutions 

 for unreduced copper and in removing copper 

 quantitatively from substances which interfere 

 with its idiometrie titration. 



6 J'. Phys. Chem.. 12, 283. 



