PoLTTEcnmc Association Proceedings. 94X 



tartrate and alkali; and third, on free tartaric acid. In the first 

 case, as soon as the current passes, only a moderate disengagement 

 of gas is produced at both electrodes, the negative becoming alka- 

 line. At the positive electrode, carbonic acid, oxygen, carbonic 

 oxyd are evolved, and a white precipitate is formed, which, by 

 analj^sis, is found to be pure cream of tartar. There is, however, 

 some tartaric acid destroyed by oxydation. The fundamental action 

 is the same in the second case, yet the results are diflerent. In 

 addition to the gases mentioned, hydride of ethylene and acetylene 

 are evolved from the positive electrode. In the third case, car- 

 bonic acid is largely predominant in the gases evolved, and acetic 

 acid is formed at the positive electrode. After the experiment had 

 been in progress for five days, the solution in the neighborhood of 

 this electrode was found to contain a large proportion of acetic 

 acid, which was separated as acetate of baryta. 



MAMMOTH GLASS PLATE. 



A single plate of glass has just been imported from France, 

 twenty feet long by sixteen feet eight inches Mide. It is used not 

 as a window, but to represent, under a strong light, a frozen lake 

 in a theatrical scene, where the professional fairies have made a 

 new sensation by displaying the "poetry of motion" on glistening 

 ice. A natural inquiry is, how such brittle material as glass can be 

 cast and annealed to this extent — why it should not fly in pieces 

 under the unequal changes of temperature to which portions of it 

 are nightly subjected ? The glass is made of such thickness as to 

 resist a very powerful blow; but the effect of unequal heating, 

 which often cracks iron plates as well as glass, is not so great as 

 might be supposed; the number of feet upon it at one time does 

 not exceed a dozen, and they are not there long enough to produce 

 any perceptible change in the temperature of the glass. There is 

 a secret connected with the manufacture of large glass plates 

 known only in certain factories in France. It is, comparatively 

 speaking, an easy task to make plates of enormous size, but to pro- 

 duce them free from cloudy spots, or, in other words, perfectly 

 transparent and homogeneous throughout, has required much time 

 and many experiments. The surmounting of difficulties yet encoun- 

 tered in other countries where glass is still too brittle, is probably 

 the result of expert manipulation, as well as the adddition of new 

 ingredients. 



