FREDERICK GUTHRIE ON THE THERMAL RESISTANCE OE LIQUIDS. 655 
same ; several weeks were thus employed. The cones were not moved during this time, 
so that even if there was a minute error in the value of (&=1 millim.) the results 
would be at all events comparable. The column of specific resistances is obtained by 
dividing the resistances of the other liquids by that of water, which of all transparent 
liquids appears to have by far the least thermal resistance. 
§ 59. With regard to the purity of the substances, they had in many cases been pre- 
pared for research by Mr. Chapman or Mr. Wanklyn (to whom I am indebted for speci- 
mens), with special view to their absolute purity. The glycerine was heated on a water- 
bath for a day, and kept in vacuo over sulphuric acid for several days. The acetone was 
prepared by myself from acetate of barium, and had been combined with sulphite of 
ammonium. The water was well boiled immediately before use. The sperm-oil was 
the ordinary commercial, which had been kept for several hours at 100° C. The alcohol 
was dried over carbonate of potassium, and twice distilled from quicklime. The nitro- 
benzol was simply dried and distilled ; it might from its history contain a little nitrotoluol. 
The amylic alcohol when dried boiled at 132° C. The oil of turpentine was commercial, 
which had been rectified. The chloroform was also commercial; it was alternately 
shaken with strong sulphuric acid and sticks of potash. The remainder, acetic acid, 
oxalate of ethyl, acetate of ethyl, oxalate of amyl, butylic alcohol, acetate of amyl amyl- 
amine, nitrate of butyl, bichloride of carbon, mercury amyl, bromide of ethylen, iodide 
of amyl, iodide of ethyl, were all either analyzed or titrated by one of the above-named 
chemists or by myself, and were shown to be of exceptional purity. The final drying 
was, wherever possible, performed by means of anhydrous phosphoric acid. 
§ 60. On account of their volatility some of these liquids might be supposed to give 
resistances too high. I was, indeed, unable to examine ether and bisulphide of carbon 
on this account. But those in the Table were seen to lose an inappreciably small quan- 
tity by vaporization, and to produce before being heated scarcely any elevation of the 
water in Q. For various reasons, it is probable that the number for iodide of ethyl is 
wrong, and that this liquid is misplaced. An idea of the amount of surface exposed 
maybe got by imagining a tube 13-4 millims. long and 1 square millimetre section, 
closed at one end, filled with the liquid and exposing therefore at the open end 
1 square millimetre. 
T =20*17 C. 
Tj=30T7 
AT =10 
h =1 millim. 
t x — 1 min. 
Thermal resistance in 
Specific 
millimetres. 
Thermal resistance. 
Water 
. . . 4T3 
1-0 
Glycerine .... 
. . . 15-85 
3-84 
Acetic acid (glacial) . 
. . . .34-63 
4s 2 
8-38 
