170 



CARNEGIE INSTITUTION OF WASHINGTON. 



the allowable current through the network is limited by heating effects in the 

 conductivity cell. The terminals of the bridge which ordinarily are con- 

 nected to the telephone are joined to the "input" of a thermionic amphfier 

 of the type used in wireless telephony and telegraphy. The telephone is 

 then connected into the output circuit of the amphfier. This arrangement 

 has resulted in effectively increasing by approximately 50 times the sen- 

 sitivity of a sensitive high-resistance telephone. Any ordinary telephone 

 becomes a more sensitive instrument with the amphfier than the best tele- 

 phones without it. 



The electron tube employed in the amphfer may also be used as a source of 

 alternating current for conductance measurements. Its advantages are its 

 cheapness and the wide range of frequencies which may be obtained with it. 

 A first harmonic is present in the current, which is noticeable at low frequencies 

 but which is not troublesome at a frequency of 1,000 cycles or more. 



If for any reason it should be desired to use frequencies in conductance 

 measurements beyond the hmit of the human ear, a telephone could still be 

 employed to indicate the bridge balance by the use of the autodyne method. 



(32) The hydrochloric-acid color method for determining iron. J. C. Hostetter. J. Am. 



Chem. Soc, 41, 1531-1543 (1919). (Papers on Optical Glass, No. 17.) 



Conditions have been found under which the yellow color developed by 

 dissolving ferric iron in hydrochloric acid may be used for the determination of 

 iron. The temperature coefficient for this color varies from 2 to 3 per cent 

 per degree, depending on the concentration of iron and probably also on the 

 acidity. The color developed by a given amount of iron varies with the acid 

 concentration, reaching the maximum intensity at from 26 to 28 per cent 

 HCl. The relative increase produced by acid is greater the higher the con- 

 centration of iron; this is especially true above 20 per cent HCl, but below this 

 concentration the relative change is independent of the iron content. Inas- 

 much as solutions must frequently be boiled in order to insure the complete 

 solution of iron present as "scale," the use of constant-boihng acid is recom- 

 mended and its use has been found to be altogether satisfactory. The effects 

 of salts on the color indicate that sulphates cause bleaching and chlorides 

 cause intensification; detailed study of the effect of the very soluble calcium 

 chloride shows that an intensification of 2.5 may be attained by the addition 

 of this salt; consequently, when testing for iron in a very soluble chloride the 

 standard iron solution must be made up to possess the same salt concentra- 

 tion. Some apphcations of the method are given and some results are 

 presented. 



(33) Ammonium picrate and potassium trithionate: optical dispersion and anomalous 

 crystal angles. Herbert E. Merwin. J. Wash. Acad. Sci., 9, 429-431 (1919). 



The dispersion and other optical properties of the substances are given. 

 The b axis of rapidly-grown trithionate crystals is longer than normal. 



(34) Equilibrium studies upon the Bucher process. J. B. Ferguson and P. D. V. Manning. 



J. Ind. Eng. Chem., 11, 946-950 (1919). 



The Bucher process is one of the processes by means of which atmospheric 

 nitrogen may be "fixed" and thereby made available for the manufacture of 

 explosives. An investigation of this process was undertaken at the sug- 

 gestion of the War Department. Experiments were made using pure chemi- 

 cals and mixtures of pure nitrogen and carbon monoxide in known proportions. 

 Curves have been obtained showing (1) the relation between the carbon 

 monoxide content of the furnace gases and the yield of cyanide, and (2) the 



