28 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[July IS, 1872. 
inaccessible places, sucli as the interior of stores or car¬ 
goes of materials liable to spontaneous combustion; of 
points elevated above the surface of the ground; or of 
purposes, or for 
great depths below for meteorological 
measuring deep-sea temperatures. 
In order to realize a pyrometer by electrical resistance, 
it is necessary to rely upon the absolute measurement of 
the electrical resistance of a coil of wire which must be 
made to resist intense heats without deteriorating through 
fusion or oxidation. Platinum is the only suitable metal 
for such an application, but even platinum wire deterio¬ 
rates if exposed to the direct action of the flame of a 
furnace, and requires an external protection. The pla¬ 
tinum wire used has, moreover, to be insulated and sup¬ 
ported by a material which is not fused or rendered con¬ 
ductive at intense heats, and the disturbing influence of 
leading wires has in this case also to be neutralized. 
These various conditions are very fully realized by the 
following arrangementThin platinum wire is coiled 
upon a cylinder of hard-baked porcelain, upon the sur¬ 
face of which a double-threaded helical groove is formed 
for its reception, so as to prevent contact between the 
coils of wire. The porcelain cylinder is pierced twice 
longitudinally for the passage ‘of two thick platinum 
leading wires, which are connected to the thin spiral 
wire at the end. In the upper portion of the porcelain 
cylinder the two spiral wires are formed into a longitu¬ 
dinal loop, and are connected crossways by means of a 
platinum binding screw, which admits of'being-moved 
up or down for the purpose of adjustment of the elec- 
trical resistance at the zero of Centigrade scale. The 
porcelain cylinder is provided with projecting rims, 
which separate the spiral wire from the surrounding 
protecting tube of platinum, which is joined to a longer 
tube of wrought iron, serving the purpose of a handle 
lor moving the instrument. If the temperatures to be 
measured do not exceed a moderate white heat, or say 
lgrade = 2372 c 
E-, it suffices to make the 
1300° Centi_ 
lower protecting tube also of wrought iron to save ex¬ 
pense. This lower portion only, up to the conical en¬ 
largement or boss of iron is exposed to the heat to be 
measured. Three leading wires of insulated copper 
united into a light cable connect the pyrometer with the 
measuring instrument, which maybe at a distance of 
some bundled yards from the same. They are connected 
by means of binding screws at the end‘of the tube to 
three thick platinum wires passing down the tube to 
the spiral ot thin platinum wire. Here two of the leading 
wires are united whereas the third traverses the spiral, 
and joins itself likewise to one of the two former, which 
torms the return wire for two electrical circuits, the one 
comprising the spiral of thin wire, and the other re¬ 
turning immediately in front of the same, but traversing 
m its stead a comparison coil of constant resistance. 
The measuring instrument may consist of a differential 
galvanometer as before, if to the constant resistance a 
variable resistance is added. If the pyrometer coil were 
to be put into a vessel containing snow and water, the 
balance of resistance between the two battery circuits 
would, be obtained without adding variable resistance to 
the coil of constant resistance, and the needle of the dif¬ 
ferential galvanometer would remain at zero when the 
current is established. But on exposing the pyrometer 
to am elevated toniperature, the resistance of its platinum 
coil would be increased, and resistance to the same 
amount would have to be added to the constant resistance 
ot the measuring instrument, in order to re-establish the 
electrical balance. _ This additional resistance would be 
the measure of the increase of temperature, if only the 
ratio m which platinum wire increases in electrical re¬ 
sistance with temperature is once for all established. 
It has been necessary to undertake a series of elabo¬ 
rate experiments m order to ascertain what is the rela¬ 
tion between the resistance and temperature in heating 
a platinum wire, with a view of finding a ratio of general 
application. Coils ot thin wire of platinum, iron, cop¬ 
per and some other metals, were gradually heated and 
cooled in metallic chambers containing the bulbs of’ 
mercury thermometers, and for higher temperatures of 
air thermometers, and the electrical resistances carefully 
noted. The progressive increase of electrical resistance 
was thus compared directly with the increasing volume 
ot a permanent gas (carefully dried) between the limits, 
of zero and 470° C. _ A formula was established according 
to which the electrical resistance is constant at the abso° 
lute zero, and progresses in a ratio represented graphi¬ 
cally by a tipped-up parabola. Although the compa- 
rison with the air thermometer could only be carried up 
to 170° C., the general correctness of this ratio has been 
verified by indirect means. 
On the occasion of bringing this subject forward at 
the Royal Institution, Mr. C. W. Siemens showed the 
■working results of the pyrometer by measuring the tem¬ 
perature of a mixture of ice and water, boiling water, 
molten lead, and the fire by which the lead was melted. 
The readings wore respectively 2° C., 98° C., 330° C. and 
860 G., the last representing a u cherry heat.” 
SORBITE, A SACCHARINE MATTER ANALOGOUS 
TO MANNITE, FOUND IN THE JUICE OF MOUN¬ 
TAIN-ASH BERRIES.* 
BY J. BOUSSINGAULT. 
Mountain-ash berries, like cherries, plums, apples ? 
etc., do not yield alcohol in proportion to the amount o^ 
saccharine matter which they contain. In a quantity o 
juice from these berries, containing 372'96 grams of sac* - 
eharine matter, and fermented under favourable condi¬ 
tions,. only 296-17 grams were decomposed, and the- 
quantity of alcohol produced was but 135 - 09 grams, in¬ 
stead ot 151*37 grams required by calculation. 
The liquid containing the undecomposed saccharine 
matter yielded a crystalline substance, having, when- 
dried, at 110°, the composition, C G H 14 0 6 , and to which the 
author has given the name of sorbite.f It is isomeric with 
mannite and dulcite, but in the form of its crystals, in its 
melting point and other properties, it differs greatly 
from both those substances. Sorbite separates from 
aqueous solution in crystals containing 2C 6 H 14 0 G .H.,0, 
which melt at 102°. The anhydrous substance melts' at 
110°-111°, whereas mannite melts at 165°, and dulcite- 
182°. Sorbite is not a fermentation, as it can be ob¬ 
tained from the juice immediately after expression._ 
Journal of the Chemical Society. 
FORMATION OF ASPARAGINE IN VETCHES, 
4 - 
BY A. COSSA. 
liiia found asparagine in vetches which had been, 
gi ow n exposed to bright light, as well as in those grown in 
darkness. Some years after Pasteur {Ann. Chim. Phijs., 
1857) grew a large quantity of vetches in the garden of 
the Academy at Strasburg, but did not obtain a trace of 
asparagine from 200 litres of the sap, whilst he found 
abundance m vetches grown in the same soil in a cellar. 
f t ^ Utll0r ’ therefore, grew some vetches in the month 
ot July, and from a kilogram of those which had been 
exposed to light, he obtained 16-25 grams of pure aspa- 
lagine, and from an equal weight of those grown in a 
cellar, he obtained 13-50 grams, the asparagine being- 
pi o\od to be identical in both cases ; similar results were 
obmnied in the months of August and September. 
1 111 a s want ot success probably arose from the cir¬ 
cumstance that the sap of vetches, especially when grown 
exposed to light, readily ferments, the asparagine being 
decomposed and ammonium succinate being formed.— 
Journal of the Chemical Society. 
* Compt. Rend., lxxiv 939-912. ~ 
f Pelouze, m 1852. (Ann. Chim. Phys. [3], xxxv, 292),. 
oo dined trom mountain-ash berries, a crystaliizable. non-fer- 
menta jle sugar, called sorbin, having the composition off 
glucose.— Pit. Journ. Chem. Soc. 
J Gazzetta Chimica Italiana, i 633-685. 
