248 Mr. R. H. M. Bosanquet on Practical Electricity. 



a question as the variation of the number of incandescent 

 lamps on a circuit. Take the case of lamps of 70 ohms. 

 Then 7 of these in parallel circuit constitute a resistance of 

 10 ohms, and 14 one of 5 ohms. Between these limits the 

 tension might be kept nearly constant by the automatic varia- 

 tion of speed above mentioned. I do not say that this is the 

 best way of attaining the result ; but with means such as I 

 possess it is a valuable auxiliary. I believe as many as 25 

 such lamps can be driven from the A machine ; but this must 

 require far greater power than is at my disposal. 



Accumulators. 



I have made 21 cells with lead plates coated with red lead, 

 and 9 of another kind, which I will describe presently. In 

 all cases the plates are wrapped in canvas. The lead I em- 

 ployed was 2 lb. to the square foot; each plate is about a square 

 foot in size ; and the red-lead plates have 1 lb. of red lead on 

 each surface. The tags at the end were left rather narrow. 

 I found lately that all the tags of the oxidized plates were so 

 eaten away at the surface of the acid that they had to be re- 

 placed. I now use lead 3 lb. to the square foot for oxidized 

 plates; the tags are left 3 or 4 inches broad, and they are 

 additionally thickened at the junctions by burning on a piece 

 of lead on each side ; they are also varnished. 



These cells were " formed " by charging in the same direc- 

 tion every day for a considerable time. The maximum effi- 

 ciency was reached in about a month, after which no further 

 improvement was perceived. 



These cells do not pretend to the excellence which is said to 

 be obtained by the cells of the Faure Company. If left 

 charged for any time, the sulphuric acid is rapidly and com- 

 pletely absorbed, leaving the water quite sweet, and consi- 

 derable quantities of sulphate of lead are formed. This is 

 slowly decomposed by fresh charging; but in the mean time 

 it appears to isolate large portions of the active material, and 

 considerably impairs the efficiency. I am informed that this 

 local action does not take place with the cells supplied by the 

 Faure Company. The red lead on the hydrogen plates becomes 

 reduced to metallic lead, and that of the oxidized plates changed 

 into black peroxide *. It is not until this change is complete 

 that the cells attain any considerable efficiency. 



* I am indebted to Mr. Fisher, of the Oxford-University chemical labo- 

 ratory, for the examination of samples of these substances. The metallic 

 character of the reduced substance was proved by amalgamation with mer- 

 cury. The peroxide contained very nearly the proper quantity of oxygen, 

 but fell a little short — not more than would be explained by inevitable 

 impurity. 



