November i6, 1893] 



A\4 TURE 



6^ 



given station, has led Dr. A. Cancani, of the Rocca di Papa 

 Geodynamic Observatory, to construct a seisnoograph which 

 registers the lime of the occurrence by an instantaneous photo- 

 graph of a chronometer. From its description in the November 

 number of L' Elettricista, it appears that the face of the 

 chronometer is photographed by the light of an incandescent 

 lamp, lighted for about a quarter of a second by a current 

 €Slab]ished automatically by the shock. A lever of the first 

 order cairies on one arm nine small vessels containing potassium 

 bichroma'.e solution, whilst the other arm rests on the armature of 

 an electro-magnet. The latter is connected to all the seismoscopes 

 of the observatory, any one of which may establish the circuit 

 and cauie the armature to be attracted down. This raises the 

 bichromate vessels and immerses the zinc-carbon couples fixed 

 above them, thus supplying the lamp with a current. The 

 closing of the circuit releases the lever, and the apparatus is 

 automatically rearranged for the next shock. 



An improved form of rotary air-pump has been constructed 

 , by Herr F. Schulze-Berge, and is described and illustrated in 

 iViedeinann s Annalen. That chief difficulty in rotary air- 

 pumps, the air-tight junction between the rotating and the 

 stationary pans, has been overcome in a manner which is 

 simple, ingenious, and very efficient. The tube from the vessel 

 to be exhausted is led through the bottom of an inclined cylin- 

 drical vessel filled with mercury. A somewhat larger tube, 

 forming the shaft of the rotating pump, reaches nearly to the 

 bottom of the vessel, and surrounds the end of the first tube in 

 such a manner ;hu there is free communication between the 

 two tubes, whilst all communication with the outer air is inter- 

 cepted by the mercury. This mercury stuffing, while causing no 

 friction, is found to be eftective even at the highest vacua. The 

 rotating tube is surrounded by another, which embraces the 

 cylindrical vessel, and revolves on it with an air-tight junction 

 formed by an ordinary stuffing-box or another mercury junction. 

 The interior of this outer tube is exhausted by an auxiliary 

 pump, so as to keep the difference of level in the mercury vessel 

 small. The shaft carries a circular tube rotating in an inclined 

 plane, about one-third of the tube being filled with mercury. 

 This mercury forms a kind of piston for drawing the air out of 

 the inner shaft, and driving it into the outer one and into the 

 auxiliary pump. The tubular ring is interrupted in one place 

 by a mercury valve, consisting of a U-tube or two concentric 

 lubes parallel to the shaft, one of which communicates with the 

 inner shaft and the recipient, the other leading into the space 

 between the two shafts. In an improved form of the apparatus 

 two concentric tubular rings are used, so that the space to be 

 exhausted is separated by the mercury valve from another ex- 

 hausted to nearly the same extent. The vacua obtained with 

 this pump are beyond the limits of accurate measurement by 

 McLeod's apparatus, and they are obtained much more rapidly 

 than by other mercury pumps. A pump with rings of 60 cm. 

 diameter and a capacity of 0*9 litre could be driven mechani- 

 cally at a speed of 15 revolutions per minute. The inventor is 

 constructing a pump of S'f litre capacity for industrial purposes. 



The E'.-::trician contains a description of a method for 

 comparing the capacities of two condensers when they are 

 of so small capacity that it is impossible to obtain, bj' the 

 ordinary direct deflection method, readings sufficiently large 

 to I e accurately measured. The apparatus used consists 

 of an electrically driven tuning-fork, performing about 2S0 

 double vibrations per second, one limb of which is pro- 

 vided with a platinised style vibrating between two light 

 platinised springs, whose movements are damped so that 

 iheir individual vibrations may not conflict with those of 

 the fork. These springs are adjusted relatively to the style on 

 the fork, so th.it contact shall be made with them alternately, 

 but that when the fork is at rest it shall not be in contact with 



either. One spring is connected to one pole of a battery, the 

 other to one terminal of a galvanometer, and the fork to oue 

 terminal of the condenser, the other terminals of the batter}', 

 galvanometer and condenser being connected together. When 

 the fork vibrates, it first charges the condenser, and then 

 discharges it through the galvanometer. The succession of im- 

 pulses being so rapid {2Sd per second], the effect upon the gal- 

 vanometer is nearly that of a continuous current, and the deflec- 

 tion is steady. It is possible with this arrangement to measure 

 the capacity of a persoa who is insulated from the floor, and to 

 note the increase of capacity due to the approach of other 

 ^uninsulated) persons to him. 



V Eleitricista for November contains a paper, by Signor 

 G. Brucchietti, on the effect of the absorption of hydrogen on 

 the thermo-electric power and electrical resistance of palladium. 

 The author finds that the resistance of a wire of palladium con- 

 taining hydrogen increases in proportion to the quantity of 

 hydrogen absorbed, and that when it is saturated the resistance 

 is 1 "55 limes as great as it was before being charged with the 

 hydrogen. If the same wire is repeatedly saturated with, and 

 freed from hydrogen the resistance seems to tend towards a 

 constant value (whether hydrogen is present or not), which is 

 intermediate between the resistance before being charged, and 

 that after being charged for the first time. In the experiments 

 on thermo-electric force the author used a couple consisting of 

 palladium and nickel, and found that the thermo-electric force 

 of this couple increased with the amount of hydrogen absorbed 

 by the palladium. When the palladium is saturated, the thermo- 

 electric force of the couple is l'66 times as great as it was 

 before the palladium was charged. In a thermo-electric couple 

 formed of charged and uncharged palladium the current at the 

 cold junction was found to go from the charged to the uncharged 

 palladium. This result is contrary to that obtained by Knott, 

 and the author supposes the divergence to be due to impurity in 

 one or other of the samples of palladium employed. 



An exhaustive study of a problem belonging to the mathe- 

 matical side of chemistry appears iii the current number of the 

 Annalcs de Chimic it de Physique. Here M. Lemoine investi- 

 gates the influence of heat, unaffected by that of light, on the 

 reactions which take place in aqueous solutions containing ferric 

 chloride and oxalic acid. When these substances are present in 

 equivalent proportions, the interaction is irreversible, and pti-- 

 ceeds according to the equation, iFeCIj — H.>C.>04 = sFeClj 

 H- 2HCI 4- 2C0._,. At any temperature the rate at which 

 decomposition takes place is found to follow the well-known law 

 of mass action, which states that the amount of substance which 

 is being decomposed at any instant is proportional to the amount 

 of unchanged substance contained in unit volume of solution. 

 The rate of change, concentration remaining the same, is found 

 to vary to a most marked extent with variation in temperature. 

 Thus at IOO^ in one hour "lo of the original amount of substance 

 was decomposed, whereas at ordinary temperatures after six 

 years only '019 equivalents had reacted. The presence of water 

 accelerates the velocity of change according to a law which 

 varies slightly wuih the temperature, a slight excess of oxalic 

 acid accelerates the rate, a large excess of oxalic acid or of 

 ferric chloride retards it. Excess of concentrated hydrochloric 

 acid almost completely arrests the reaction. The efi'ects whicli 

 these and other materials exert upon the course of the simple 

 reaction, the author studies both by chemical and thermochemi. 

 cal methods, and shows that they may be explained by the 

 occurrence of secondary reactions. The communication, which 

 extends over more than 100 pages, serves to give some idea of the 

 patient labour involved in elucidating the mechanics of what 

 appears at first sight to be a comparatively simple case of 

 chemical decomposition. 



NO. 1255, VOL. 49] 



