In an experiment made on charging the reservoir in the motor, the pressure in the fixed reservoirs, at the time of charging the reservoirs on the motor, was 63.8 atmospheres, at a temperature of 68° F. One atmosphere was lost by letting the air into the pipe laid between the shed and the tramway where the motor stood; when the reservoir on the motor was charged, the pressure fell to 42.6 atmospheres in the fixed reservoirs, at a temperature of 55° F.
The pressure in the reservoir on the motor, when ready to start, was 42.6 atmospheres, at a temperature of 84° F. On its return, at the end of forty-six minutes, after a journey as above mentioned of about three and a quarter miles including the triangle, the pressure had fallen to 20.9 atmospheres, and the temperature to 71° F. The weight of air used during the journey was thus about 110 lb., or, say, 34 lb. per mile. The coal consumed by the stationary engine to compress the air amounted to 39 lb. per mile, in addition to 3 lb. of coke per mile for warming the exhaust.
While the motor was performing its journey, the stationary steam-engine was employed in raising the pressure in the fixed cylinders to 63 atmospheres, and worked, on an average, during fifty minutes in each hour; during the rest of the journey it remained idle. It was thus always employed in doing work in excess of the pressure which could be utilized on the car, and the work was, under the circumstances of the case, necessarily intermittent. This was a very unfavorable condition of working.
In the electric tram-car the haulage was effected by means of accumulators. The car was of the ordinary type with two platforms. It was said to have been running as an ordinary tram-car since 1876. It had been altered in 1884 by raising the body about six inches, so as to lift it clear of the wheels, in order to allow the space under the seats to be available for receiving the accumulators, which consisted of Faure batteries of a modified construction. The accumulators employed were of an improved kind, devised by M. Julien, the under manager of the Compagnie l'Electrique, which undertook the work.
The principal modification consists in the substitution, for the lead core of the plates, of one composed of a new unalterable metal. By this change the resistance is considerably diminished, the electromotive force rises to 2.40 volts, the return is greater, the output more constant, and the weight is considerably reduced. The plates being no longer subject to deformation have the prospect of lasting indefinitely. The accumulators used were constructed in August, 1884.
The car, as altered, had been running as an electric tram-car on the Brussels tramways since October, 1884, till it was transferred to the experimental tramway at Antwerp. The accumulators had been in use upon the car during the whole of this period, and they were in good order at the end of the experiments, that is to say, when the exhibition closed at the end of October, 1885.
The accumulator had forty elements, divided into four series, each series communicating, by means of wires fixed to the floor of the car, with commutators which connected them with the dynamo used as a motor.
There were two sets of these batteries or accumulators, one of which was being charged in the shed while the other was in use. The exchange required ten minutes, including the time for the car to go off the tramway into the shed and return to the tramway. This exchange took place after every seven journeys. Therefore, the two batteries would have sufficed for working the car over a distance of about forty-two miles during sixteen hours.
It may be observed that the first service in the morning would be performed by means of the accumulators charged during the afternoon and evening of the previous day.
Each element of a battery was composed of nineteen plates, of which nine were positive, four millimeters thick, and ten negative, three millimeters thick. Each positive plate weighed 1.44 lb., of which about twenty-five per cent. consisted of active material. Each negative plate weighed nearly 1 lb., of which one-third consisted of active matter. The weight of the metallic part of the battery amounted, therefore, to 1,846 lb.; and the whole battery, including the case and the liquid, amounted to 2,464 lb., which contained 499 lb. of active matter, or about 20.25 per cent. The four cases in which the battery was contained were so arranged as to divide the weight equally between the wheels.
Two commutators inclosed in a box were placed on the platforms at the two ends of the carriage, so as to be available for moving in either direction.
The accumulators were divided into four series of ten double elements, which, by means of the commutators, could be united under four combinations, viz.:
1st. 4 series in quantity - 1 in tension. 2d. 2 " " " 2 " 3d. 3 " 4th. 4 "
Finally, a fifth movement united the four series in quantity, coupling them on each other, and putting the dynamo out of circuit, thus restoring equilibrium. When in a state of repose, the handle was so arranged as to keep this latter switch turned on. The accumulators were arranged for charging in two series united in quantity, each containing twenty double elements. The charge was effected by a Gramme machine, worked by a portable engine. Each of these series received its charge during seven hours for the ordinary service of the car, and during nine hours for the accelerated service.
The accumulators on the car actuated a Siemens dynamo, acting as a motor, such as is used for lighting, having a normal speed of 1,000 revolutions, fixed on the frame of the carriage. The motion was conveyed from the pulley on the dynamo by means of a belt passing round a shaft fixed on movable bearings to regulate its tension, and thence to the axles by means of a flat chain of phosphor bronze. The chain was adopted as the means of moving the axle, on account of its simplicity and facility of repair by unskilled labor.