152 Scientific Intelligence. 



heat is produced on the addition of alkali. The heat thus meas- 

 ured (q 1 + q + -f q n ) which is the total heat of combina- 

 tion, is one quarter of that which the weight of the acid taken, p 9 

 would evolve. From the equation E = 2000 p / 400 n = 5 p / n 

 the equivalent of the acid E can be obtained, approximate to 

 1 / nth. Obviously the quantity of alkali added at first should 

 not be sufficient to neutralize all the acid taken, since in that case 

 P»P& etc - become zero. If the more accurate determination of 

 the equivalent be desirable, a repetition of the experiment is 

 made, using acid of the same strength but a potash solution only 

 1/I0th as strong; the result in this case being approximate to 

 w/l0th. With monobasic acids the values of g x , q 2 , etc. are 

 equal ; with many polybasic acids they differ among themselves, 

 decreasing with the successive additions of alkali. The equiva- 

 lent of a base is fixed in a similar wav, these rules applying only 

 to soluble acids or bases yielding soluble salts. — Ann. Chim. 

 Phys., VII, vii, 283, February, 1897. g. f. b. 



4. On the Action of Potassium and Sodium vapor in coloring 

 the Haloid salts of these metals. — The blue color produced by the 

 action of the cathode rays on crystals of sodium chloride, so 

 similar to blue rock salt, has suggested to Giesel the feasibility 

 of coloring such crystals by purely chemical methods. In fact 

 by heating the crystals with the vapor of sodium or potassium in 

 a closed tube, color is readily developed, the particular color 

 being independent of the metal employed. Thus treated, potas- 

 sium bromide and iodide are colored deep blue ; potassium chlor- 

 ide dark heliotrope and sodium chloride yellow to brown, the 

 color appearing to permeate the whole crystal. It is permanent 

 in the air, and also in water so long as the crystal is undissolved. 

 The solution is colorless and gives a colorless residue. On heat- 

 ing, the color disappears. The yellowish brown sodium chloride 

 however, when heated, becomes gradually yellow, red and bluish 

 violet and finally colorless; but by cooling at any particular 

 stage the color then possessed becomes permanent. So that a 

 shade of blue may be thus obtained identical with that of the 

 natural rock salt. — Per. Perl. Chem. Ges., xxx, 156, February, 

 1897. Kreutz claims to have obtained this result in 1892. — lb. 

 p. 403. G. E. B. 



5. On the Action of the Silent Electric Discharge on Helium. 

 — The conditions under which helium will enter into combination 

 have been studied by Berthelot. The method used as well as 

 the apparatus were the same as those employed in the case of 

 argon, the graduated tubes permitting the measurement of 5 CC of 

 gas to 1/200 and even to 1/500 of a cubic centimeter. Comparative 

 experiments were made with nitrogen, argon and helium. Placed 

 in a closed tube over mercury and submitted to the electric dis- 

 charge for 12 to 15 hours, neither of these gases either combined 

 with the mercury, suffered any molecular condensation or devel- 

 oped fluorescence. In presence of benzene vapor, however, nitro- 

 gen developed fluorescence and disappeared in a few hours. Argon 



