Dr. Tyndall. On Carbonic Acid and Bisulphide of Carbon. 129 



DESCRIPTION OF PLATE 1. 



1. Effect of pyrogallic acid solution upon the red blood-corpuscles of the newt, 



2. Effect of gallic acid. 



3. Effect of hydrochloric acid. 



4. Effect of oxalic acid. 



5. Effect of carbolic acid. 



6. Various forms assumed by the corpuscles when acted upon by ammonium 



sulpliocyanide or potassic sulphocyanide. 



7. Various forms produced by the action of ammonium chromate. 



8. Shows final effect of ammonium sulpliocyanide on the nucleus, viz., to reveal 



an intranuclear plexus. 



April 5, 1883. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. " On a hitherto unobserved Resemblance between Carbonic 

 Acid and Bisulphide of Carbon." By John Tyndall, 

 F.R.S. Received March 15, 1883. 



Chemists are ever on the alert to notice analogies and resemblances 

 in the atomic structure of different bodies. They long ago indicated 

 points of resemblance between bisulphide of carbon and carbonic 

 acid. In the case of the latter we have one atom of carbon united 

 to two of oxygen, in the case of the former one atom of carbon united 

 to two of sulphur. Attempts have been made to push the analogy 

 still further by the discovery of a compound of carbon and sulphur 

 analogous to carbonic oxide, but hitherto, I believe, without success. 

 I have now to note a resemblance of some interest to the physicist, 

 and of a more subtle character than any hitherto observed. 



When, by means of an electric current, a metal is volatilized and 

 subjected to spectrum analysis, the "reversal" of the bright band of 

 the incandescent vapour is commonly observed. This is known to be 

 due to the absorption of the rays emitted by the hot vapour in the 

 partially cooled envelope of its own substance which surrounds it. 

 The effect is the same in kind as the absorption by cold carbonic acid 

 of the heat emitted by a carbonic oxide flame. For most sources of 



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