Description of the Steam Pyrometer. 103 
989.6 x 990 
672° 
=1462° above the boiling point, or 1674° of Fahrenheit’s scale. 
The process of calculation may be much simplified, when the spe- 
cific heat of the standard piece has been accurately ascertained and 
its equivalent of water found; for we have then only to multiply the 
weight of steam produced by its latent heat, or heat of elasticity, 
and divide by that equivalent. ‘This is the same as multiplying the 
weight of steam by a known constant fraction. In the fifth experi- 
ment above cited, the equivalent of the metal is 672 grains of water, 
so that the constant fraction by which to multiply the weight of steam 
actually generated, in any given experiment with that cylinder of iron, 
in order to obtain the temperature above 212°, is 222=188, or (in 
decimals) 1.4732. This number, multiplied by 780, gives the de- 
grees 1149, as before. ‘The process may be farther abridged, by 
performing the multiplication by logarithms, in which case we should 
have the logarithm of 1.4732 constant, and hence it would only be 
necessary to find in the table the logarithm of the grains of steam, 
add it to said constant quantity, and find the number standing against 
their sum, for the temperature above 212°. 
Thus, the logarithm of 1.4732 is .168259 
To which add the logarithm of 780 = 2.892095 
And we obtain the logarithm of 1149° = 3.060354 
It will be no less easy to solve the same problem by means of a 
Gunter’s scale and a pair-of compasses. The distance from 1 to the 
constant fraction, (1.4732 in the above case,) on the line of numbers, 
will reach from the number of grains of steam to the temperature, 
in degrees Fahr., above 212°. 
We might, instead of determining the specific heat of the stand- 
ard mass, by the ordinary methods, first heat it to a known tempera- 
ture in boiling mercury, in oil, spirits of turpentine, melting zinc, lead, 
bismuth, tin, or any convenient alloy* of these metals, and then ob- 
grains of vapor; consequently its heat must have been 
* The alloys of tin and lead are very convenient for this purpose. Their mel- 
ting points as determined by M. Kupffer, (See Ann. de Chim. et de Phys. XL. 
302; and Thomson on Heat and Electricity, p. 174.) are as follows: 
Alloy of 
Tin Lead Point of fusion. 
1 atom + 1 atom - - - 466° 
y_) + Ee Saye be 385 
3 «c + 1 cc 2 Pe us 367 
ie 7 RR as Bi “00s 372 
5 are Gp ha ate eh eee ae 
The alloy eaten employed by tin plate workers is I believe composed of 1 tin, 
-++2 lead. The meanof several trials with that alloy have convinced me that its 
melting point is 385°. 
