222 Scientific Intelligence. 



f—f 

 unity for moderately dilute solutions, ^ =0-01. Therefore if 



the relative diminution of the vapor pressure be divided by the 

 number of molecules of substance existing in 100 molecules of the 

 solution, a quotient of 0*01 is obtained, whatever be the character 

 of the dissolved substance. If R molecules be dissolved in 100 



molecules of ether, N= — — ^ ; and replacing N in the last 



100 4" lv y? j>l -i 



equation by its value thus obtained, we have „^L = =^. In 



^ J ' /R 100 + R 



proportion as R decreases, or the solution becomes more dilute, 



• f—f 

 the ratio J' tends toward - 01 ; reaching it when R = l appar- 

 ently. Hence if one molecule of a substance be dissolved in 100 

 molecules of ether, the vapor pressure of the ether is diminished 

 by a fraction of its original value which is nearly constant and 

 which is sensibly equal to 0*01. If m be the mass of the sub- 

 stance dissolved in 100 grams of ether and M be its molecular 



mass 74 being the molecular mass or ether, — = — =- r — 



N /•_/" 100 100XM + 74XW; 

 and since as above stated — = — —--, where K=l, we have for 



100 / fm 



the value of the molecular mass M=0'74 -^ — -,. Of course this 



value is approximate only ; but if the boiling point of the dis- 

 solved substance is above 140° and not more than 20 grams of 

 it be dissolved in 100 of ether, it is sufficient to enable the mole- 

 cular mass to be fixed as between multiple values. Thus the 

 molecular mass of turpentine thus determined, is 132 ; of aniline 

 87 ; of ethyl benzoate 159*2 : and of benzoic acid 124*6 ; in place 

 of 136, 93, 150 and 122 the true molecular masses. In general 

 the author regards his cryoscopic or fusing point method as pref- 

 erable ; though in special cases the present method is evidently 

 useful. — Ann. Chim. Phys., VI, xv, 375, November, 1888. 



G. F. B. 



2. On a Method of Avoiding " Bumping " in Distillation. — 

 Markownikoff has suggested the use, in place of platinum wire, 

 charcoal, etc., introduced into solutions to prevent bumping dur- 

 ing ebullition, a few thin capillary glass tubes 3 to 10 mm in 

 length sealed at one end. Under these circumstances the boiling 

 goes on quietly, both at the ordinary and at reduced pressures, 

 even when a finely divided precipitate like barium sulphate ex- 

 ists in a saline aqueous solution. Even caustic soda solution may 

 be made to boil quietly in this way. Branner recommends that 

 the tubes be made of different sizes so as to float in different 

 layers of the liquid. For the distillation of concentrated acids he 

 has found this method invaluable. — J. Gh. Soc. Musse, 1887, 520 : 

 J. Chem. Soc, liv., 1155, Nov. 1888. g. f. b. 



3. On Thiophosphoryl fluoride. — Thorpe and Rodger have 

 published a preliminary notice of a new gas, thiophosphoryl 

 fluoride, PSF S . It is obtained by heating phosphorus pentasul- 



