SCIENTIPIC NEWS. ^ 33 1 



jecture, that water must contain some combustible 

 matter; 



If two substances be mixed of known refractions and The propor- 

 prpportiottS, and regard be had to the density of the *'°" o^P^^sin 

 mixture, the total refraction may be calculated ; and, on pounds, if 

 the other hand, when the refraction of a mixture of transparent, 

 which the element^ are known is ascertained, their pro- ^fjg^ from*^*^ 

 portion may also be had. Mr. Delambre, in his report, thdrrefractive 

 explains the principles of this calculation. power. 



Mr. Biot having applied it to mixtures of known pro- 

 portions, and having always found it just, has made use 

 of it to determine the unknown proportions of other 

 mixtures. 



For this purpose it is only needful to fill a prism of Method of 

 glass, under a known pressure, with the substance jn. n^^l^^^ng "i« 

 tended to be examined; or, to form a prism of it, if it 

 be solid, through which a remote object is to be ob- 

 served; the angle of refraction is to be measured with 

 the circle of repetition, keeping an account of the pres- 

 sure, the heat, and the humidity of the external air; 

 and this method being susceptible of a precision equal to 

 that of astronomical processes, necessarily surpasses all 

 our chemical processes in accuracy. But it must also be 

 remembered that it is applicable only to transparent 

 substances, of which the principles are known as to their 

 nature or species. 



It is particularly useful to give perfection to the analy- particularly 

 sis of gasiform substances, and Mr. Biot has already applicable to 

 obtained interesting results in this respect. le gases. 



Oxigen refracts the least, and hidrogen the most, at 

 equal densities. The refractions of the same gas are 

 strictly proportional to its densities when the tempera- 

 ture is constant. Strongly refracting substances appear 

 to owe their force particularly to hidrogen, for they all 

 contain it. Atmospheric air gives exactly, by experi- 

 ment, the refraction which, according to calculation, Common air 

 ought to be produced by a mixture of 2!0 oxygen, 787 ^^^^^^^^^""^^^ 

 azote, and 3 carbonic acid. The application of the rule 

 is found to hold not only in simple mixtures, but in more 

 intima,te combinations, provided no very considerable 

 condensation has been produced. Thus ammoniacal gas 

 " y y 2 produces 



