814 REPOET- 1886. 



a cell, but is dependent on the treatment the cell receives in use and the extent to 

 which the ahove action is appreciated. The buckling of the plates was stated 

 to be due to insufficient charging, which allowed a hard enamel of sulphate of lead 

 to form on the surface of the active material. It was also found that charging 

 tended to soften and remove this enamel. The falling out of the active material 

 was generally due to the hard sulphate mentioned above, which caused the plugs 

 ■of active material to split and come out of the plates entire. If, again, the dis- 

 charge was too rapid there was a tendency for the active material to scale off, and 

 a fine disintegration of the oxides showed that the plates contained insufficient 

 sulphate, which acted as the binding agent. Some curves were exhibited showing 

 the result of recent tests made with standard type 15-plate boxes, which gave a 

 commercial efficiency of 90 per cent, in ampere-hours and 80 per cent, in watt- 

 hours, allowing throughout the experiment about an hour's charge after gases were 

 given off, so as to keep the plates in order. These figures were the mean of six 

 consecutive charges and discharges at a constant current. It was found that with 

 a drop of 10 per cent, in E.M.F. the capacity was over 400 ampere-hours, and a 

 discharge of 9 hours at a rate of 25 amperes showed a drop of only '02 of a volt. 

 The maximum capacity claimed for these cells by the maker was found to be 

 reached with a drop of E.M.F. of under 5 per cent, in the case of the cells under 

 test. The instruments used were carefully calibrated, the amperes being measured 

 by frequent readings from a Siemens dynamometer checked from time to time by a 

 voltameter, which agreed within 1 per cent. The volts were taken with a high- 

 Tesistance reflecting galvanometer calibrated by standard Olark ceUs and freshly 

 made Daniel cells. 



7. Electric Lighting at CannocJc Chase Collieries. By A. Sopwith. 



This paper must be considered as merely introductory to a visit which was pro- 

 posed to be made by members of the Section to the Cannock Chase Colliery, and 

 dealt in a general way with some special advantages and economies in connection 

 with the electric lighting of collieries. 



The author pointed out the convenience and economy in utilising the ventilating 

 fan engines for working dynamos, on account of the regularity of speed (which 

 apart from the requirements of an installation is kept within a limit of from 1 to 3 per 

 cent., such variation being a gradual diminution or increase) and the fact that such 

 engines run continuously night and day. The fan itself acts to some extent as a 

 regulator, as the tendency to run away on switching out of lights is modified by 

 the increasing resistance of the air ; vice versa the putting on of load and consequent 

 tendency to slacken speed is reduced by the diminished work done by the fan at a 

 few revolutions less ; again the comparatively small proportion of power required for 

 working the dynamo, amounting to from 7 to 12 per cent, of the usual working 

 power of engine, may be considered an advantage. 



Tbe addition of counter-shafting in cases of slow running fans, or single pulleys 

 in case of quick running fans, is an easy and inexpensive matter. 



Allusion was made to the small extra consumption of coal in practice, and the 

 merely nominal value of the slack which is consumed. In further connection with 

 the working expenses, viz. replacement of lamps, it was mentioned that the under- 

 ground workings in vicinity of shafts (extending to 200 or 300 yards) admit of lamps 

 being worked considerably below power with sufficient effectiveness, and actual 

 lives were given (including breakages) showing at one pit an average of 2,270 hours. 

 The men who are required to act as examiners of machinery, and have no specifically 

 regular work to do otherwise, replace lamps, andean attend to any occasional work 

 connected with installation. As a matter of fact the three installations now 

 working at Cannock Chase have not necessitated the employment of an extra man. 



The only original feature — at least the author presumes it to be so — is the 

 utilisation of old iron and steel pit ropes for main and branch cables. From four 

 to five miles of rope are worn out annually, varying from |"to 1^" diameter and over, 

 and the conductivity of this has been proved to be about one-seventh that of a 

 copper cable (of high conductivity) of similar dimensions. In the case of shafts, 



