13 Improvements in Physical Science (JAN. 
iiber die Phosphorescenz und die Farben. (Schweigger’s Journal, 
xiv. 133.3 xv. 172.) 
2. Homlerg’s Pyrophorus.—About seven years ago Sir H. Davy 
announced that Homberg’s pyrophorus owes its peculiar properties 
to a quantity of potassium reduced during the formation of the sub- 
stance, and which evolves potassureted hydrogen when it comes in 
contact with moisture. Some years ago Dr. Coxe, of Philadelphia, 
maintained a similar opinion in a letter which I published in an 
early number of the Annals. Dobereiner has lately noticed this 
opinion of Dr. Coxe, and endeavoured to show by some experi- 
ments that the substance formed, and to which the pyrophorus owes 
its peculiar properties, is a compound of potassium, sulphur, and 
carbon. (Schweigger’s Journal, xvi. 118.) 
VII. HEAT. 
1. Dilatation of Bodies by Heat.—MM. Gay-Lussac and Arago 
_ have published in the Ann. de Chim. et Phys. various tables of the 
dilatation of bodies by heat. Ishall insert here such of these tables 
as are not already familiarly known to the English reader. 
Tasrie I.—Linear Dilatation of different Substances when raised 
from the Temperature of freexing Water to the boiling Heat of 
that Liquid, according to the Experiments of Laplace and 
Lavoisier. 
Dilatation for a length = 1. 
Fo Ben, 
n 
Substances. In Decimals. Vulgar 
Fractions. 
Steel not tempered ..... ROE eae O°00107915 .... sty 
Steel tempered, and then heated to 250°.. 0°00123956 .... s4> 
Silver from the cupel ..........2-.- 9°00190974 .... ste 
Silver, Paris standard .........-..+: O°CO190868 .... ste 
Copper a. «ia sles « p ETRE ES Serie o- O00171733 «42. ss 
I ee ake cared tan « be Dass He eee O-O018782ZE | ew ae 
"Tin from Malacea, + 5 2:-..50.0 os.e0.40f0.5,0 6 O°00193765 sani oe 
Tin from Cornwall. .)... 6.50.00. ojo ¢ O02 1 7-208 5 os x ae 
Hammered iron. .....5..:»- 03 Serta as 0°00122045 .... <4) 
BOON AEC Sts n'a 07 vies a> sie(h oeete tains 0°00123504 .... <1, 
English flint glass ....... Sh Pee 0°00081166 .... 255 
Mercury (in volume). ..+.+.+e0++++- O'01847746 .... song 
Pipe colds <artane’ aes iene pd sat 0°00146606 .... <4; 
Gold, Paris standard, not annealed .... 0°00155155 .... g4; 
Gold, Paris standard, annealed ...... O°00151361 .... gy 
Platinum (according to Borda)........ 0°00085655 .... +455 
Lead, .\j6e8 be punttcvee +f wits bem aletet owas tubs A) OOZR4 SEB is ai sti 
French crystal glass ,......+. papas NegOIDOURZ USS oan acetems 
French grown glass .....+-+0+ oese+ 0°00089694 ....+415 
French mirror glass ........ nse dager Ce ODUSDORD -<5:. : 
