Prof. Dove's Experiments hi 'Electricity and Magnetism, 225 



85° C, deposits a red crystalline precipitate of red oxide of 

 copper, which dissolves completely in muriatic acid. In this 

 way he found, that on the conversion of starch into dextrin 

 and so into grape sugar, not a trace of gum is formed as inter- 

 mediate product; if a precipitate was obtained, it resulted from 

 undecomposed starch, which might be easily recognized by 

 the addition of an aqueous solution of iodine. If a solution 

 of grape sugar and of potash be treated so long with a solu- 

 tion of the sulphate of copper as the separated hydrate of the 

 oxide of copper is redissolved, in a very short time a precipi- 

 tation of the red oxide of copper takes place at the common 

 temperature; if the sokition is warmed the red oxide is imme- 

 diately separated, even when a small quantity of the sulphate 

 of copper has been employed, and the liquid soon becomes 

 colourless ; a liquid containing y;J^ of grape sugar gives, 

 when boiled, a perceptible precipitate; and when it contains 

 , ,)„„ „„„ , a distinct red colouring is seen when the light is let 

 fall on it. A solution of cane sugar with potash, treated with 

 the sulphate of copper, becomes of a deep blue; it can be 

 boiled, when potash is used in excess, without any separa- 

 tion of the red oxide of copper, which results only after con- 

 tinued boiling, or when left to stand for several days ; but even 

 after several weeks the whole of the oxide has not been reduced. 

 Milk sugar acts like grape sugar. This method is of impor- 

 tance in detecting small quantities of grape sugar in the chyme, 

 chyle and blood ; the author had not been able to detect any 

 in the latter. — [Ann. der Chem. und Pharm. xxxix. p. 360. 



XXXII. Experiments in Electricity and Magnetism. By 

 Professor H. W. Dove of Berlin*. 



1 . On the Induced Currents excited by the Magnetization of 

 Iron by means of Frictional Electricity. 

 ¥ F in two wires, a b and c d, which 

 are coimected by the wire b c, 

 we excite an electric current, this 



current when tlisappearing will in- " ^ 7 ^ 



(.luce in two neighbouring parallel a. b ~ 3 



wires an electric current having the same direction. If, how- 

 ever, we connect these wires crosswise, then the a ~b 

 currents induced in a|3 and y S by the primary •'■ f 

 currents in ub and cd will act exactly contrary { li ^ 

 to each other, and there will be a perfect equi- ^^ V I J ,j 

 iibrium; if, however, near to ab there is another nl 



* Extracted from a letter from Professor Dove, and coinmunicateil by H. 

 Croft, Esq., Teacher of ('hemistry. 



P/iil. Mag. S. 3. Vol. 20. No. 130. March 18V2. Q 



