18 
Remarks on Daniel’s Hygrometer . 
[Jan. 
IV . — Remarks on Daniel’s Hygrometer , Is connected with the Purity 
and Strength of Ether in India. 
To the Editor of Gleanings in Science. 
MR, 
In a paper of mine, on Hvgrometry, published in your second number, p. 46, occurs 
the following passage : “ But there is a still more serious objection to the use of 
Mr. Daniel’s Hygrometer in India. It is the almost total want of action under which it 
labours, owing to the impossibility, I suppose, of keeping our ether in any thing like 
a state of purity in temperatures, which for some part of the year exceed that of its 
boiling point, and for the greater part are not removed 10° from it. It is evident 
that no stopper will coniine the vapour of ether in a temperature of 96° ; even at 86, 
it exerts a force equal to 25 inches of mercury. Accordingly, I have never yet been 
able to obtain a correct result with it. So far from the depression reaching the dew- 
point, which is, I believe, occasionally, even 60° below the temperature of the air, I 
have never been able, however liberal of my ether, to obtain a greater depression 
than 60°. ” 
A friend, who had purchased a Daniel’s Hygrometer with its supply of ether, the 
property of the late Dr. Abel, and who knew me to be the author of the above paper, 
expressed his surprise at this statement, which he declared to be entirely contradict- 
ed by his experience. He suggested that the ether I had used might have been im- 
pure, i. e. a mixture of alcohol and ether, in which case my explanation would apply ; 
but that it was not applicable to good or pure ether, which might be diminished in 
quantity, but could not be deteriorated in quality, by any evaporation. He offered 
to convince me, by actual experiment, that, even "in the dampest weather, ether would 
produce, in India, a depression of 30 or 40°. 
1 he ether I had used, and to which the above extract refers, was of three different 
sorts ; I first tried part of a stock which belonged to a chemical test chest. Thinking 
this might possibly have been filled up in the country, I wrote for some to England: 
it was no better. I next tried some that had been procured from the Honorable Com- 
pany s Dispensary it had no more power than either of the others. I was then led 
n°f [°" clu ® lon above suited, that the best ether of commerce must he a mixture 
of alcohol and pure ether, and that the latter, evaporating in consequence ofthe l.Sh 
air was 86°, the moist-bulb thermometer marked 80° \v, temperature of the 
effect of the ether I had before used r Z , 8 ° e be S an b Y trying the 
M 2*. We then tried of the L- 
but very little. When that belonging to the instrument hi a llttle more effect » 
pression became suddenly much jrreater -md in f 5 °' v ^ ver > was used, the de- 
with dew. The temperan!^ seconds the ball was covered 
temperature of the air, and this in very damp welZZ^H ' 4 ° ° r l2 ° be,ow the 
pushed farther with the hygrometer m T n i l, i f \ 6 . r,le experiment was not 
in a still more striking inlnne", ' arid L Zt l \ ^ diffei * e nce of the ethers 
some guide as to judging of the value of eth \ " 1' lat tbe resu lts might furnish 
hygrometry. ° ° ° ' aluL °‘ cth<il wh <i“ required for the purposes of 
poisr, 
the ,,our ° 
80° 
was used for this pur- 
pom ed on it, and the maximum 
In the case 
temperature of the lu „ W(UI ux A/ - u 
show the difference of tbe two liquids I npvt AIUS was sufficient W 
73 .being 13° below the temperature ofthf ■ tr ed a rcr Y strong brandy it -are 
ether. This further strengt Std Va'"' V ° f ‘^effect of th Aad 
Wp tUre 0t , alcob()1 and ether, in which the latte^h ° ther 1 had b °en using was 
error ? dr ‘"’’ th .f foll °"'i°S conclusions from but * srat ‘» proportion 
Th°k^J"?! >ose hat K» Cther l be “ I. Vtitfe* 
om these experiinents” 
be kept even in a terr 
in India: Ts^IT 0 " 8 \* nd the conclusion, ttt 
a, is p , 0 tanto invalidated. 2. That ordinarj 
for to suppose that pure & ether m , S "T thes{ 
DaniePg'pj ygrometer h 'ZESfr * eVneouT" ? > mperature of 
