PROCEEDINGS OF THE POLYTECHXIC ASSOCIATION. 541 



Mr. Rouse said that the greatest difficulty in getting good 

 workmen was on account of the short apprenticeship they served. 

 He thought that a seven years apprenticeship was little enough 

 to make an apprentice proficient in the art. Instead of their 

 serving that time he found it ver}'- diffi.cult to get young men to 

 remain longer than three years in his employment as apprentices. 



Mr. Johnson wished that the first half-hour of the next meet- 

 ing would be devoted to Mr. Davis, for the purpose of allowing 

 him to express his views on the subject of pottery. 



Adjourned to Thursday evening, Jan. 17, at half-past seven 

 o'clock. 



American Institute, Polytechnic Association, ) 

 Ja7iuary 17, 1861. \ 



Professor Mason in the chair. 



Dr. Van der Weyde said, in reference to the subject of " the 

 difiereiit methods of using electricity to ignite inflammable sub- 

 stances " : 



The idea of lighting inflammable substances by means of elec- 

 tricity is not new ; the ignition of alcohol, ether, gunpowder, &c., 

 by the electric spark, is one of the oldest experiments in that 

 branch of physics ; later the power of galvanic currents in heat- 

 ing this metallic wire has been used for blasting purposes, and 

 also for lighting candles, lamps, &c., and finally the sparks of gal- 

 vanic induction currents have been used to light gas. 



Some patents have been taken out for those purposes, and it 

 may be interesting to give here the several methods in the same 

 order as I did give them to demonstrate to my class in chemistry 

 in the Cooper Institute, in this city, this kind of practical use 

 made of electricity. 



1. The spark of a common electric machine, igniting all kinds 

 of inflammable substances, solid, as rosin, gunpowder; liquid, as 

 alcohol, ether ; gases, as hydrogen, carburet of hydrogen, &c. 

 This is an application almost 100 years old, and now repeated in 

 all courses of Natural Philosophy. 



2. The small spark of the clectrophorus. Some 50 years ago 

 small apparatus were for sale, when by only turning the stop- 

 cock of a hydrogen gas jet, a small spark, produced by a perma- 

 nently charged clectrophorus ignited the hydrogen and this a 

 lamp and candle. Such an apparatus I have in the collection of 



