276 Mr. Daniell on a New Register-Pyrometer^ 



which does not differ quite yo.uoo^'^^ '^^ ^" ^"*^^ from the 

 foregoing mean. 



Having thus, I trust satisfactorily, established the accuracy 

 of the pyrometer, and the degree to which confidence may 

 be placed in its indications, I shall conclude this part of my 

 subject with the details of some experiments upon the fusing 

 points of different metals. I shall designate the registers of 

 coarse and fine-grained black-lead respectively by the letters 

 A and B. 



Exp. 7. About 30lbs. of the clippings of thin sheet copper 

 were very gradually melted in a crucible in the blast furnace 

 of the Royal Institution. The platinum bar was adjusted in 

 the register B, and when the metal was about half run down, 

 it was placed perpendicularly with the index upwards in the 

 crucible, and held down with a pair of tongs. The crucible 

 was then gradually fed with the clippings till the melted metal 

 covered about two-thirds of the register. In this situation it 

 was kept ten minutes, and when it was lifted out some of 

 the metal remained unmelted. A crust of oxide, mixed with 

 metal, had also affixed itself to the upper part of the black- 

 lead. This was partially dissolved away and loosened by im- 

 mersing the i-egister with great care, when cold, in a diluted 

 mixture of sulphuric and nitric acids. The whole was thus 

 easily removed, and the black-lead exhibited a perfectly clean 

 surface. The arc measured upon the scale was 5° 49', de- 

 noting an expansion of '0508. The temperature of the labo- 

 ratory was about 65°. 



I am indebted to the kindness of Mr. Mathison for unex- 

 ceptionable opportunities of taking the melting points of gold 

 and silver at the Royal Mint, who also most obligingly assisted 

 me in the operations. Two new registers were prepared, which 

 I shall designate as II. and III. : their rates of expansion 

 were not determined till after the experiments. 



Exp. 8. The register II. was carefully adjusted with the 

 platinum bar. About 90lbs. of fine gold were weighed, and one 

 of the ingots was cut into ten pieces for the purpose of gra- 

 dually feeding the crucible, and keeping the temperature down 

 to the true melting point during the observation. The re- 

 mainder was melted in a black-lead crucible in a wind-furnace. 

 When just fused, one of the pieces was thrown in, and the 

 melted metal immediately congealed upon the surface. The 

 register, which had been slowly heated in another crucible to 

 a dull red, was then taken up with a pair of tongs and plunged 

 perpendicularly into the gold about two-thirds of its height. 

 In this situation it was kept ten minutes, and during the time 

 two more lumps of the metal were thrown in. It was then 



carefully 



