﻿160 Scientific Intelligence. 



When intermediate in strength, both actions may go on together 

 and the gas appear to be unchanged. — Ber. Berl. Chem. Ges., 

 xix, 1099-1106, May, 1886. G. f. b. 



2. On the Combustion of Cyanogen. — Dixon has studied the 

 conditions under which a mixture of cyanogen and oxygen gases 

 is exploded and has reached the conclusion that the explosion 

 depends solely upon the nature of the spark itself. The spark 

 from the Holtz machine failed entirely to explode dry mixtures 

 of these gases. The induction spark failed to explode the mix- 

 ture in the eudiometer where the wires were 0*25 to l mm apart ; 

 but the explosion was violent in the tubes when the wires were 

 1 to 3 mm apart, and this was quite as true when the gases were 

 moist. He then compared the explosion rate of this mixture 

 with that of carbon monoxide and oxygen, using for the pur- 

 pose a tube ten feet long and recording the time on a pendulum- 

 chronograph. The velocities obtained were as follows in meters 

 per second : cyanogen and oxygen, dried with phosphoric oxide, 

 813, dried with KOH 808, saturated with moisture at 15°, 752. 

 Carbon monoxide and oxygen dried with P 2 5 , 36 ; with H Q S0 4 , 

 119; saturated with moisture at 10°, 1*75 ; at 35°, 244; and at 

 ■60°, 317. It is noticeable that in the latter case the explosion- 

 rate increases rapidly when a trace of moisture is added to the 

 mixture ; while in the case of cyanogen the presence of water 

 vapor causes a slight fall in the rate. When a platinum wire is 

 heated in the cyanogen mixture to dull redness, the coil cooled 

 without result when the circuit was opened. But when raised to 

 full redness it glowed brightly for half a minute .after the 

 current was broken and orange fumes were observed in the tube. 

 About three-fourths of the cyanogen had been converted into 

 C0 2 and one-fourth into CO. — J. Chem. Soc, xlix, 384-391, 

 May, 1886. G. f. b. 



3. On the so-called Critical Pressure in Solids. — v. Bjchter has 

 discussed the phenomenon of the non-fusibility of solids under cer- 

 tain conditions of pressure. Lothar Meyer had shown that iodine 

 may be fused by heat or not according to the pressure upon it. 

 Carnelley, who studied the same phenomenon in ice, regarded the 

 fusion as conditioned upon a certain minimum pressure, which he 

 called the "critical pressure," and which he defined as that 

 external pressure at w^hich no amount of heat will fuse the solid. 

 According to Pettersson, the critical pressure of a substance is 

 the pressure at which the boiling point of its liquid and the 

 melting point of the solid coincide. The author reasons that as 

 a liquid can exist as such only when the pressure upon it is 

 greater than the tension of its vapor at that temperature, it 

 follows that a fusible solid under a less pressure than the vapor 

 tension at the fusing point cannot be melted, but on heating will 

 pass directly into the state of vapor. A solid body, then, will 

 evaporate without fusing whenever the pressure upon it is less 

 than the vapor tension at the fusing point. Hence he suggests 

 that the term "fusing-point tension" is a better term than 



