On the Destructive Distillation of Animal Substances. 145 



collars might also be useful in case of accidental fracture of that 

 part of the instrument. 



If an accident happens to Daniell's instrument, the injury is 

 irreparable ; but if a thermometer or collar happens to give way 

 in the hygrometer under consideration, the damage is easily set 

 right at a trifling expense. The same brass stopper will always 

 answer again. 



I ought to have mentioned formerly, that a little key of brass, 

 to be fitted, when required, into the ivory collar at 0, is employed 

 in screwing and unscrewing the ivory collar ; and that the other 

 extremity of this key may be inserted with advantage into the 

 neck of the little brass bottle, to aid in the same operations 

 regarding the bottle. 



In cold and dry weather in winter it is very essential that the 

 aether should be the very best commercial aether, and probably 

 fresh aether used for each observation. In summer, the superior 

 excellence of the aether is by no means so important ; and the 

 used aether of winter might be kept in a properly stopped bottle 

 for summer use, with a slight addition of fresh aether, as formerly 

 explained. Spare leather washers ought to accompany every 

 instrument. These often require change, to adjust the relative 

 positions of the brass bottle and syringe. 



I omitted also to mention formerly, that when an accurate 

 observation has been accidentally missed at first, or when from 

 any cause it is wished to repeat an observation, the temperature 

 ought to be allowed to rise 8° or 10° above the point to which it 

 has fallen, before it is again slowly reduced ; because as soon as 

 the exhaustion is stopped, the comparatively warmer air heats the 

 exterior surface of the bottle faster than the liquid and the ther- 

 mometer are heated ; and if the cooling is not again begun from 

 8° or 10° higher than the temperature has fallen to, the dew- 

 point would be got too low, the surface taking some time to cool 

 again. 



I have the honour to remain, 



Your very faithful Servant, 



A. Connell. 



XX. On the Products of the Destructive Distillation of Animal 

 Substances. — Part III. By Thomas Anderson, M.D., Regius 

 Professor of Chemistry in the University of Glasgow*. 



IN the preceding parts of the investigation of the products 

 obtained by the destructive distillation of animal substances, 

 I have entered fully into the method of treating the raw material, 



* From the Transactions of the Royal Society of Edinburgh, vol. xxi. 

 part 1 ; read April 17, 1*51. [Part I. appeared in the September Number 

 of this Journal for 1848; Part II. in our Number for December 1851.] 



Phil. Mag. S. 4. Vol. 9. No. 57. Feb. 1855. L 



