6 Mr. G. Gore on the Development of Dynamic Electricity 



must now be passed into the water, and as soon as the tempera- 

 ture of the water and upper plate begins to rise, and the needles 

 of the galvanometer to be deflected, the direction of the deflections 

 must be noted every few minutes until the temperature of the 

 water reaches 205° or 210° F. If a verification of the result is 

 required, the water may be allowed to cool gradually, and the 

 deflections noted as it cools, or what is much better, the experi- 

 ment may be wholly repeated. The current of steam should be 

 of such an amount as to raise the temperature of the water from 

 60° to 210° F. in two and a half or three minutes. 



15. The time required to make a single examination of a 

 liquid varies from ten minutes to half an hour, according to the 

 facility of manipulation; liquids which act strongly upon the 

 washers or plates, such as strong acids or alkalies, or those which 

 exhibit ii-regular phsenomena, require much longer time, and 

 need several examinations to verify the result. 



16. Many precautions are necessary to be observed in the 

 construction and use of the apparatus in order to exclude every 

 interfering circumstance ; the washers should be of such a nature 

 as not to act chemically upon the metal plates ; they should also 

 not give way and be forced out by the combined influence of the 

 heat and pressure; vulcanized india-rubber washers, covered 

 with a thin sheet of ordinary india-rubber on the side next the 

 plates by means of a solution of india-rubber in bisulphide of 

 carbon, answer admirably after having been used a few times ; 

 or vulcanized india-rubber ones alone succeed well with some 

 metals after much use, but not in examining strong nitric acid, 

 because of its action upon them. The only washers I have found 

 to withstand this liquid with the heat and pressure, were formed 

 of a layer of asbestus-fibre stuck upon the ends of the cylinder 

 by means of a little shell-lac varnish. Washers formed of ordi- 

 nary india-rubber or of gutta-percha only last during a single ex- 

 periment, — the heat and pressure combined spoil them. Leather 

 washers soaked in shell-lac varnish and dried, succeed for a few 

 expeiiments, but soon become hard and brittle ; and they are 

 unfit for examining strong mineral acids or alkalies, being acted 

 upon by them. Washers of calico, linen, or flannel, soaked in 

 varnish and dried, quickly become hard and break. Of whatever 

 material the washers may be composed, they should be perfectly 

 alike, and be well cleaned from any previous liquid before each 

 experiment. 



17. The metal plates should be as homogeneous and alike as 

 possible, and if made of cast metal, each must be cast at the 

 same pouring ; each should be smooth and clean, polished with 

 the same materials and in the same manner; the most scrupu- 

 lous care must be taken to have them equally smooth, and the 



