A new Fact in Galvanism. 203 



view methods by which the last could be counteracted j but 

 I saw no remedy for the first. I began, therefore, to de- 

 spair of ultimate success with tubes of porcelain *. 



Another circumstance confirmed me in this opinion. I 

 found it impracticable to apply a heat above 27° to these 

 tubes, when charged as above with carbonate, without de- 

 stroying them, either by explosion, by the formation of a 

 minute rent, or by the actual swelling of the tube. Some 

 times this swelling took place to the amount of doubling 

 the internal diameter, and yet the porcelain held tight, the 

 carbonate sustaining but a very srriall loss. This ductility 

 of the porcelain in a low heat is a curious fact, and shows 

 what a range of temperature is embraced by the gradual 

 transition of some substances from a solid to a liquid state ; 

 for the same porcelain which is thus susceptible of being 

 stretched out, without breaking, in a heat of 27°, stands the 

 heat of 132°, without itijury, when exposed to no violence, 

 the angles of its fracture remaining sharp and entire. 



[To be continued.] 



XXXV. A new Fact in Galva?iism. Communicate^ ly a, 

 Correspondent. 



To Mr. Tilloch. 



SIR, 



W ISHING to promote Galvanic inquiries (when unattended 

 with cruelty), 1 shall beg the favour of you to insert in your 

 Magazine the following circun)stanccs, which I do not know 

 have been observed before : 



In trying to produce the nervous flashings by resting dif- 

 ferent parts of the face on a cylinder of wood covered with 

 tin -foil, I was surprised by perceiving, when the no^e was 

 on this cylinder, that there was a strong disagreeable smell, 

 like that which is produced in making inflammable air (hy- 



• I am nevertheless of opinion, that, in some situations, experiment: witl^ 

 compression may be carried on with great ease and advantage in such tubes. 

 I allude to the situation of the gcclofjists of France and Gerniaiiy, who may 

 fasily procure, from their own manufactories, tubco of a quality far superior 

 lo any thing made for sdle in this country. 



drocca 



