P ROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 975 



of Philadelphia, (No. 62,876,) in which he claims the use of the 

 electricity developed by the friction of a steam jet when blowing 

 from a boiler, like from a safety-valve, collecting this electricity 

 outside the boiler by means of the metallic brush (usual for this 

 purpose in the steam electric machine, invented some thirty jcaxs 

 a^o,) and communicating it to the shell. 



There are, however, tAVO reasons why this principle cannot 

 be expected to work successfully. In the first place, we do not 

 want the intensity currents — it is not friction electricity, or so 

 called static electricity, which can determine the direction of 

 deposits from liquids; but we want the quantity currents, devel- 

 oped by the simple evaporation, or by chemical action — the so- 

 called dynamic electricity — which determines the direction of 

 such deposits, and is nsed in electro-plating, etc. In the second 

 place, these steam electric machines work never for any length of 

 time satisfactorily, but the most perfect ones give out in a few 

 hours, even sometimes in a few minutes, requiring to be stopped, 

 regulated, re-arranged, cleaned or repaired, which defects have 

 always been the objection to their introduction as generators of 

 electricity, like every one knows who has ever been bothered with 

 using them. 



From the preceding account it is evident that the static elec- 

 tricit}', which manifests itself alone l)y sudden discharges and 

 sparks, (Parry's last patent,) is useless; also, that the galvanic 

 electricity produced by two metals plunged in the same liquid 

 (Webster and Young's patent) is injurious, as it not only prevents 

 the incrustation, but dissolves the boiler itself (the remedy being 

 worse than the disease.) What we want is a simple electric repul- 

 sion l)etween the shell of the boiler and the particles of solid 

 deposit, so that these are prevented from adhering to the boiler. 



To settle this matter I made a series of experiments about the 

 electricity of deposits, and found, by causing them to settle on a 

 small metalic plate placed on the bottom of a porcelain evaporat- 

 ing dish, that most deposits are positive electric, which was ascer- 

 tained by having an isolated wire attached to the plate, and this 

 being connected with an electrometer, the last indicated positive 

 electricity, when, after heating the dish, the liquid Avas loft to 

 cool and crystalize or deposit. The same facts Avere also proved 

 by Pouillet in France, and recorded in the Anales de C/mnie et de 

 Physique, second series, tome xxxvi., p. 4. 



When positive electricity was discharged from this metallic 



