r24 



SCIENCE 



[Vol. LVI, No. 146©- 



instead of bemg colloidal. That is, they are 

 j'ellow crystals. Contrary to some previous ob- 

 servations rhythmio bands of the silver chromate 

 form in darkness at 0° C. and room temperatures. 



Ferric oxide liydrosol. II. The chlorine and 

 hydrogen ion activities and the heat of coagula- 

 tion with sodium sulfate: Fkedeeick L. Browne. 

 A study has been made of the hydrogen and the 

 chlorine ion activities in ferric oxide hydrosol 

 and in hydrolyzed and unliydrolyzed ferric chlo- 

 ride solutions. From these data the distribution 

 of FeCls and HCl between the dispersed phase 

 and the dispersion medium has been computed. 

 When the heat of coagulaition of these sols with 

 Na2S04 is corrected for the heat of mixing of 

 N,a2S04 with the FeOls and HCl present, there 

 is left a small positive heat effect which is pro- 

 portional to the amount of Na2S04 adsorbed dur- 

 ing coagulaition and amounts to about 1,200 eal. 

 per g. eq. Na2S04 adsorbed. 



Ferric oxide hydrosol: Arthuk W. Thomas and 

 Alexander Fkieden. 



A note on quinaldine pinlc: Hans T. Clark and 

 Felix A. Elliott. 



The coagulation and repeptisation of colloidal 

 ferric hydroxide iy allcalis: Robert E. Wilson 

 and Philip S. Clark. In order to improve the 

 efficiency of removal by filtration of small 

 amounts of colloidal ferric hydroxide from hot 

 water which has been passed over sheet iron to 

 remove dissolved oxygen, a study was made of 

 various passible coagulating agents for ferric 

 hydroxide. It was found that alkalis were by far 

 the most effective precipitaiting agents in small 

 amounts, and that as low as .05 per cent. jSTaOH 

 effected practically complete coagulation in a very 

 short time. Larger amounts of alkali were found 

 to decrease the efficiency of filtration, and this 

 behavior was eventually shown to be due to the 

 repeptization of the ferric hydroxide as a nega- 

 tive colloid, with markedly different properties. 



Gum dammar as an emulsifying agent: Harry 

 jSr. Holmes and Donald Cameron. Since gum 

 dammar is insoluble in water but soluble in 

 many other liquids its use as an emulsifying 

 agent forces water to become the internal or dis- 

 persed phase in the " water-in-oil" type of emul- 

 sion. Such emulsions are more stable and may 

 be made much richer in water than by the use of 

 calcium soaps. Salve-like emulsions are readily 

 made by mixing a solution of the gum in benzene 

 with a relatively large amount of vaseline or 

 heavy oil and then rubbing in the desired amount 

 of water. Printers' or lithograph inks may be 



greatly cheapened by the incorporation of vrater, 

 dispersed in minute drops, by the use of this gnm 

 as emulsifying agent. Since much of the drying 

 oil is used merely to give a proper working body, 

 the use of water, well emulsified, will give the 

 requisite body more cheapl}' while a smaller 

 amount of the drying oil is adequate for adhesive- 

 purposes. Paints, varnishes and greases may be 

 diluted in similar fashion. 



Cupric oxide jellies and the general theory of 

 jelly formation: Harry B. Weiser. A dilute col- 

 loidal solution of hydrous cupric oxide is formed 

 by adding ammonia short of precipitation to a 

 saturated solution of cupric acetate. This col- 

 loid coagulates on standing, forming a gelatinous 

 precipitate of the hydrous oxide. By adding a 

 suitable small amount of sulfate to the acetate 

 solution before adding ammonia, a more concen- 

 trated colloidal solutdon of hydrous cupric oxide 

 may be prepared. This colloid is likewise instable 

 and, under suitable conditions, coagulates with 

 tJie formation of a stable jelly. The sharply de- 

 fined conditions of formaftion and the effect of 

 electrolytes on the stability and rate or precipi- 

 tation of the eolloddal oxide support the author's 

 general theory of the formation of inorganic 

 jellies proposed at the Birmingham meeting. 



A rapid method for the preparation of some 

 dilute silica gels: L. H. Keyerson and Wm. T. 

 MORIN. It has been found that ammonium hy- 

 droxide solutions will under certain conditions 

 cause solutions of sodium silicate, mixed with 

 hydrochloric or sulfuric acids, to set to gels. 

 Using this method it has been possible to set gels 

 with an SiOo concentration as low as approxi- 

 mately one half of one per cent. Gels as low as 

 two per cent. wUl set almost instantly. The ehai- 

 aeteristics of these dilute gels are being studded. 



Studies on the nature of the reducing action of 

 charcoals on certain salt solutions. I. Silver 

 nitrate: L. H. Reteeson and Mas Latshaw. The 

 reducing action of various charcoals upon silver 

 nitrate solutions has been studied. An almost ash- 

 less charcoal was prepared in order to eliminate 

 the interferences due to impurities. Neutralization 

 of surface charges does not account for the reduc- 

 tion to metallic silver. Evidence from Hulett "s 

 work as well as our own investigations points to 

 the fact that an active form of hydrogen, strongly 

 adsorbed by the charcoal, is the reducing agent. 

 Silica gel outgassed at 400 C. and cooled in an 

 atmospliere of hydrogen reduces silver ion in 

 silver nitrate solutions to silver. This reaction is 

 being studied in its effect on various cations, . 



