bservations on Mr. Smith's Experiments on Fermentation. 39 



the angle between normals to the faces p pf increases about 

 44' : m m' does not perceptibly change. 

 The symbols of the simple forms are 



h {100}, / {oio}, o {ooi}, y {HI}, 



P {101}, s {201}, * {102}, m {110}. 



No other forms were observed. 



The optic axes lie in a plane parallel to the face /, and, in 

 air, appear to make with each other an angle of 8 40'. The 

 minimum deviations of the brightest rays of the spectrum 

 refracted through the faces m, m" are 24 15' and 38 49', 

 for light polarized in planes respectively perpendicular and 

 parallel to the intersection of the faces m, m". Hence the 

 velocity of the brightest rays of the spectrum in air divided 

 by the velocities within the crystal, will be 1'5052, 1*5046, and 

 1*333, for rays in planes parallel to k, I, o, polarized in those 

 places respectively. 



St. John's College, Cambridge, June 4th, 1840. 



VII. Observations on Mr. Smith's Experiments on Fermenta- 

 tion. By R. RIGG, F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 

 GENTLEMEN, 



HPHE reading of Mr. Denham Smith's paper printed in the 

 Number of your valuable Periodical for March, entitled, 

 " Observations on the supposed Formation of Inorganic Ele- 

 ments during Fermentation," induces me to ask you the fa- 

 vour of saying, through the same publication, that in the abs- 

 tract of my paper on that subject, which is noticed by that 

 gentleman, the increase in the quantity of earthy and alkaline 

 matter therein mentioned, does not apply to the original 

 quantity contained in both the refined sugar and the yeast 

 employed in my experiments, but to that in the former only. 

 The latter previous to using being deprived of its soluble 

 matter by repeated washings in cold water, loses very little, 

 if any, of its solid materials when employed in promoting the 

 vinous fermentation. 



It may be added that the circumstances which I have found 

 most favourable for ihe formation of these bodies during 

 this chemical action on refined sugar, are when the sugar at 

 the commencement forms about 20 per cent, of the weight of 

 the mixture, and when about nine-tenths of this dissolved 

 body has undergone decomposition by a quick process, the 



