66 Scientific Intelligence. 



and only sparingly soluble in water. Both funnels are then 

 shaken up for two minutes, care being taken to avoid rise in tem- 

 perature, and they are allowed to settle for half an hour. A plug 

 of cotton wool is placed in the tube of each funnel, and after 

 drawing off l cc or so, the rest of the filtered aqueous layer is col- 

 lected in a small flask and well closed. In this aqueous solution 

 the phenol is estimated by titration with bromine; 10 ec of the so- 

 lution being placed in stoppered bottles along with 25 oc of bro- 

 mide-bromate solution and 10 cc of 10 per cent hydrochloric acid. 

 After half an hour 10 co of solution of potassium iodide (42 g. pr 

 liter) is added and in 15 minutes the solution is titrated with 

 twentieth normal thiosulphate solution. From the above equa- 

 tion 



M s =ri25# s 94/10 . L (L — L). 



The author obtained for benzene values for the molecular mass 

 ranging from 74-7 to 80'1 (theory requiring 78) ; for chloroform 

 from 95-9 to 120'0, and for vinyl tribromide from 257*5 to 294 ; 

 theory requiring 1I9'5 and 2G7 respectively. — Ber. Berl. Chem. 

 Ges. ,'xxvii, 324, 328, February, 1894. g. f. b. 



2. On the Use of 'the Lummer- Brodhun prism in Colorimetry. 

 — The Lummer-Brodhun prism which has proved of so much ser- 

 vice in photometry has been applied by Kritss with equal satis- 

 faction, in colorimetry. This double prism consists of one ordi- 

 nary total reflecting prism with its hypothen use-surface plane, 

 and of a second such prism having its hypothenuse-surface spher- 

 ical, with the exception of a small circular plane surface at the 

 center. The second prism is so adjusted to the first that its plane 

 circle is in the center of the plane hypothenuse side of the other, 

 the two being pressed together so as to leave no air between 

 them. The double prism thus obtained permits light to pass un- 

 changed through its central contact surfaces, while those rays 

 which are incident upon the outer portions of the plane surface 

 are totally reflected. It follows that the transmitted beam ap- 

 pears as a central luminous circle while the totally reflected one 

 is a bright ring surrounding it. If the central image and the an- 

 nular one are given by different sources of light the point where, 

 on moving away the brighter source, the intensities become equal, 

 can be very exactly determined. In Kriiss's colorimeter, the light 

 traversing the prism comes through the one solution, and that re- 

 flected by the prism through the other; the arrangement of auxil- 

 iary prisms being such that each ray has to pass through an equal 

 thickness of glass and suffer the same number of reflections. — 

 Zeit. anorg. Chem. v, 325, November, 1893. g. p. b. 



3. On Electrolysis by Alternating Currents. — An investigation 

 has been untertaken jointly by Hopkixsojst, Wilsox and Lydaix 

 in order to determine first, the energy dissipated by the so-called 

 electrolytic hysteresis, and second, the quantity of an ion per 

 square centimeter of an electrode, required to change the proper- 

 ties of the electrode to that of the ion during alternating current 



