^4 Ohfervattons upon art ttnnfnal 



perly, it is the adion of the acid, and not that of the oxy- 

 gen, which the alkali neutralilcs. I have freed the latter 

 entirelv from thefe inconveniencies by receiving the ether on 

 liquid an^imonia, which is burnt by the oxygen in propor- 

 tion as it comes in contaft with it: but this manipulation is 

 accompanied with too many dangers for me to venture to 

 recommend it in general. 



Another method of feparating the ether from the oxygen- 

 ated acid would be, to receive this liquid on water ; to re- 

 move it in proportion as it floats on the furfjce, by means of 

 a fvphon or pump ; to fliake it with the alkaliae folution; 

 and to decant it again on pure water. You then obtain the 

 whole ether, which may be afterwards feparated from the 

 water bv reftification. 



Ether, freed in any manner from its acid, mufl finally be 

 mixed with twice its bvilk of water, and rcdilicd at a heat 

 equal to that of Guyton's economical furnace. 



A marine ether may be compofed by one operation if you 

 diftill, at a boiling heat, a mixture of alcohol and the oxy- 

 genated muriat of potafli in the proportion of I'oo to O'l^. 



It is not necelfary to recommend to thofe who are ever fo 

 little habituated to this kind of labour, to cool, from time to 

 time, in the colirfe of the dillillation, the receiver, by apply- 

 ing to it a wetted fponge. 



VI. Objervaiions upon an unujual horizontal RrfraSiion of 

 the Air j luilh Remarks on the Variations to ivhich the 

 lourer Parts of the Atmofphere are fometimes fubje£l. By 

 the Rev. S. ViNCE, A.M. F. R.S. and Plumtan Profejfor 



of AjhoKomj and experimental Phihfophj in the Univerjity 

 of Cambridge * . 



Jl he uncertainty of the refraftion of the air near the 

 horizon has long been known to aftronomers, the mean re- 

 fraftion varying by quantities which cannot be accounted for 

 from the variations of the barometer and thermometer j on 



• From the 'Triinjailions of the Royal Society for 1799. 



which 



