176 Prof. Schoenbein on a tiew Test for Ozone. 



In this instance, the force employed, corrected as before for 

 the friction of the pulleys, was equal to raise eOSO*^ lbs. to the 

 height of one foot. 



In estimating the capacity for heat of the apparatus, it was 

 necessary in this instance to obtain the specific heat of the 

 sperm oil employed. For this purpose I employed the method 

 of mixtures. 43750 grs. of water were heated in a copper 

 vessel weighing 10403 grs. to 82°-697. I added to this 28597 

 grs. of oil at 55°" 593, and after stirring the two liquids 

 together, found the temperature of the mixture to be 76°'583. 

 Having applied to these data the requisite corrections for the 

 cooling of the liquids during the experiment, and for the capa- 

 city of the copper vessel, the specific heat of the sperm oil came 

 out 0*45561. Another experiment of the same kind, but in 

 which the water was poured into the heated oil, gave the spe- 

 cific heat 0'46116. The mean specific heat was therefore 

 0-45838. 



The weight of oil employed was 70273 grains, and the 

 paddle, can, &c. were the same as employed in the first series 

 of experiments ; consequently the entire capacity in this in- 

 stance will be equivalent to that of 35951 grs. of water. The 

 heat evolved was therefore 7°'7747 when reduced to the ca- 

 pacity of a pound of water. 



Hence the equivalent deduced from the friction of sperm 

 oil was 782" 1, a result almost identical with that obtained from 

 the friction of water. The mean of the two results is 781*8*, 

 which is the equivalent I shall adopt until further and still 

 more accurate experiments shall have been made. 



XXXI. Letter from Prof. Schcenbein to Prof. Faraday, 

 F.E.S., on a neiso Test for Ozo7ief. 



My dear Faraday, 



HAVING a good opportunity for sending you a few lines, 

 I will make use of it to tell you something about my 

 little doings. You are no doubt struck with the peculiarity 

 of the ink in which this letter is written, and I am afraid you 

 will think it a very bad production ; but in spite of its queer 

 colour, you will like it when I tell you what it is, and when I 



* This number is slightly different from 775, the equivalent stated at 

 Oxford, and used by me as one of the data for calculations on the velocity 

 of sound. The reason of the difference was that by an oversight 1 had 

 taken the friction oiboth pulleys as the correction of each weight instead 

 of both weights. The whole of the experiments are exactly the same as 

 those presented to the Oxford meeting. The slight alteration in the equi- 

 valent will make only a very trifling alteration in the theoretical velocity 

 of sound given in the last Number of this Magazine. 



t Communicated by Professor Faraday. 



