September 13, 1889.] 



SCIENCE. 



new form the salts remain white if they are kept out of the light, 

 no change whatever in color appearing on mixing the mercurous 

 ■sulphate with the zinc sulphate. This result is secured by the 

 greatest care in making the mercury salt. It is found that a mer- 

 curous sulphate can be made so free from the mercuric form that 

 it does not turn yellow when all the acid is washed out. 



Professor Carhart says, in a letter to Queen & Co. of July 8, 

 1889, " Sent you six new standard Clark cells, numbers 106, 107, 

 108, 109, no. III. The extreme difference between these cells 

 when only four days old was only 0.0006 of the electromotive force 

 of the cell, and they were still approaching one another. There 

 was a difference of only 0.0003 between five of these, and only 

 o.oooi between four of them." Again, referring to six cells, not 

 made in the latest secure form for transportation, which were sent 

 by express from Ann Arbor, Mich., to Queen & Co.'s laboratory 

 in Philadelphia, and returned to Ann Arbor, a journey of over 

 fourteen hundred miles, he writes, " After letting the cells rest 

 thirty-six hours I am much gratified to find that their extreme differ- 

 ence from one another is only 0.08 per cent, and the average of the 

 six cells is only 0.08 per cent lower than my standards kept here." 

 These are remarkable results from such a severe test as this, but 

 the latest form will make a still better record. 



A new process of sealing the cell is also employed. Marine 

 glue, which was recommended by Lord Rayleighas a sealing mate- 

 rial, always gave trouble to secure a firm hold on glass and to 

 prevent air bubbles from being inclosed to such an extent as to 

 greatly weaken the seal. Its viscosity was also such that any small 

 internal pressure, due to heat or the generation of a little gas, was 

 liable to force the cell open. With the new compound employed 

 'the closure remains perfectly firm, and forms an entirely satisfac- 

 tory hermetic sealing. 



These cells are all set up by Professor Carhart in the physical 

 Jaboratory of the University of Michigan, and are furnished with 

 his personal certificate, giving the electromotive force of the cell, 

 its temperature coefficient, and guaranteeing each cell " provided 

 no current greater than 0.00002 ampere be passed through it, and 

 provided it be subjected to no violent mechanical strain or jar." 

 With even a larger current than the above, these cells show no 

 polarization whatever in five minutes, and with ten thousand ohms 

 external resistance a polarization of only o.oi per cent is observed 

 in this time. The cell recovers from this small polarization, which 

 is less than the usual accidental differences between different 

 cells, in five minutes or less. The errors arising from ignorance 

 of the exact temperature of the cell are greater than any liable to 

 occur from polarization. To guard against accidental short-cir- 

 cuiting. Queen & Co. are motinting a graphite resistance of about 

 twenty thousand ohms in circuit with the cell and inside the case 

 which incloses it. These cells are mounted in handsomely finished 

 brass cases, 3I inches high and 2f inches in diameter, with an en- 

 graved hard rubber top, giving the number of the cell correspond- 

 ing with the certificate, indicating the positive and negative poles, 

 and having a hole for the insertion of a thermometer to ascertain 

 the temperature in the inside of the cell. Batteries of these cells, 

 in any number desired can be mounted if required. 



Boissier Dynamos for Plating and Lighting. 



The dynamos shown in the accompanying illustrations possess 

 some features of novelty, invented and patented by Mr. Herman 

 Boissier, electrician of the Arnoux & Hochhausen Electric Com- 

 pany of this city. The aim of the inventor was to produce a dy- 

 namo of low first cost, not liable to get out of order, and so simple 

 in construction that it would require no more attention than could 

 be given it by any workman of average intelligence in plating or 

 electrotyping establishments. The favor with which the machines 

 have been received and the flattering testimonials of those who 

 use them would seem to indicate that the dynamos approximate 

 very closely to the inventor's ideal. 



The machine shown in Fig. i occupies a floor space of only six- 

 teen by twenty-six inches, and weighs about a hundred and thirty- 

 five pounds, of which only about thirty-five pounds are copper. 

 It furnishes current for twenty-five sixteen-candle-power lamps, or 

 a proportionate current of lower voltage when wound for plating 

 purposes. Owing to the peculiar method of winding the armature. 



there are only four sections to the commutator. Fig. 2 shows a 

 form of dynamo made specially for use in electrotyping establish- 

 ments, and furnishing a current of very low voltage. The field 



FIG. I. — BOISSIER DYNAMO. 



coils are composed of copper ribbons alternating with ribbons of 

 insulating material. The armature, shown in Fig. 3, is composed 

 of heavy copper bars passing round a cylinder of insulated soft 



FIG. 2, — BOISSIER DYNAMO. 



iron wire. All insulating material on the armature is fire-proof, so 

 that it is impossible that the armature should ever burn out. Two 

 of these dynamos are in use in the government printing office at 



■^«=r- 



FIG. 3.— ARMATURE OF PLATING DYNAMO. 



Washington, in the electrotyping department, where they have a 

 record of three hundred ounces of copper deposited in two hours, 

 using one machine only. They are manufactured by the Arnoux & 

 Hochhausen Electric Company. 



