406 Mr. Brooke and Mr. R. Phillips ofi an apparent 



of a congregation of 500 people assembled for two hours with 

 50 candles burning; the air completely neutralized 150 grains 

 of lime water, but took very little more ; this accords nearly 

 with 1 per cent, of carbonic acid gas. The oxygen was not 

 examined. 



1824, November 28. — Examined the air at the close of an 

 ordinary congregation, perhaps 200 people, retained for two 

 hours. 



Average of five experiments gave the oxygen 20*42 per cent. 



1826, March 16. — Examined the air from a crowded con- 

 gregation after two hours' confinement, but some doors open. 



Average of four experiments gave the oxygen 20*23 per 

 cent. 



There was a very slight appearance of carbonic acid each 

 time a charge was passed up through lime water, a phaeno- 

 menon never observed in ordinary atmospheric air. 



The general conclusions, it seems to me, to be drawn from 

 these experiments are, that the proportion of oxygen to azote 

 in the atmosphere on the surface of the earth is not precisely 

 the same at all places and times ; and that in elevated regions 

 the proportion of oxygen to azote is somewhat less than at 

 the surface of the earth, but not nearly so much so as the 

 theory of mixed gases would require ; and that the reason for 

 this last must be found in the incessant agitation in the at- 

 mosphere from winds and other causes. 

 June 6, 1837. 



LXVI. Note 071 an apparent Case of Isomorphous Substitution, 

 By H. J. Brooke, Esq,, F.R.S. 



To Richard Phillips, Esq., F.RS, 

 My dear Sir, 

 T SOME time since pointed out the very near identity of 

 *- the forms, cleavage, and angular measurements of zoizite 

 and euclase, but I omitted to refer to their apparently ana- 

 logous chemical composition. 



Silica. Alumina. ' Lime. Glucina. Protoxide. 



Zoizite (Klaproth) 43 , 29 , 21 , 3 



Euclase (Berzelius) 43-22, 3056, 2178 222 



This is apparently a case of isomorphous substitution, but 

 on pointing it out lately to a chemical friend he observed, that 

 the proportion of glucina in euclase was 2 atoms, while the 

 lime in zoizite was only 1 atom, and that the identity of form 

 must therefore be accidental ; but if this be so, may not all 

 other cases of isomorphous substitution ( I do not allude to 



