'i98 On preparing Potatoes in Digesters 



and amber mixed. Carbon darkens these shades, and con- 

 veys at times some very fine tints of colour, approaching to 

 the fire of" the ruby or the mellowness of the topaz. An 

 extra dose of carbon destroys the transparency, and throws 

 a cloudiness over the fracture of a blue wavy cast, always at- 

 tended by the elevation of minute globules of iron upon the 

 surface of the glass. 



There is now only one thing that occurs to me that can 

 be urged against the foregoing conclusions. It appears, 

 that in proportion as the carbonates are free from iron, their 

 fusion per se affords glass proportionably transparent ; and 

 in the case of the pure lime the result was nearly as trans- 

 parent as water. If therefore the deduction formerly drawn, 

 that the disappearing carbon unites not with the lime, but 

 with the iron, be correct, the glasses, after the whole of the 

 metal is discharged, ought to approach the transparency 

 and purity of the fusions per se. The reverse is however 

 the fact; for in no stage of these experiments do the respec- 

 tive glasses exhibit a less degree of transparency than after 

 the iron is discharged. I cannot decidedly account for this ; 

 but I am inclined to think that this permanent lead blue 

 colour arises from a peculiar combination of iron with cal- 

 careous earth, experienced in a great many experiments 

 with iron and steel. 



[To be continued.] 



LII. Experiments on preparing Potatoes in Digesters for 

 feeding lean and fattening other Stock. By the Rev. 

 William Pierrepont, of Burton Park, Sussex. 



J. HE thanks of the Society for the Encouragement of Arts, 

 Manufactures, and Commerce, from the 21st volume of 

 whose Transactions we copy the subjoined particulars, were 

 voted to Mr. Pierrcpont last session for the following com- 

 munication : 



'' SIR, 



" The object of the Society for the Encouragement of 

 Arts, &c. being the general benefit of the community, I 

 send 3-ou the following method of preparing potatoes, for 

 the purpose of both feeding lean and fattening other stock ; 

 conceiving and hoping, from the experiments I have already 

 made, that it will contribute something to the end which 

 the society has in view. Not altogether satisfied with the 

 system of curing or preparing potatoes by steam from heated 



water. 



