154 Mr. L. Hun ton on the definite Combinations 



duced to examine further, and found that though the solution 

 when heated in an open shallow vessel, as a watch-glass, may 

 be alternately raised to ebullition and cooled, for several times 

 in succession, without forming any permanently insoluble pre- 

 cipitate, yet if heated but once, or twice at the furthest, in a 

 deep narrow-mouthed vessel, as a test tube, a separation of 

 protoxide takes place. The presence of free or uncombined 

 sugar is also of much consequence, for if we add a little to 

 any of the saturated solution and then heat, insoluble prot- 

 oxide is formed even in a watch-glass ; on the contrary, a free 

 alkali appears to retard the deoxidation in the test tube, and 

 to prevent the formation of a little which takes place after 

 four or five heatings in a watch-glass, and resulting from the 

 formation of a little carbonate of lime, and consequent setting 

 free of sugar. 



If instead of boiling, a few test tubes are filled with the so- 

 lution, a result variable with the difference of exposure and 

 presence of free sugar is obtained ; thus, 



In open tubes. In closed tubes. 



No. 1. Solution alone. No. 4. Solution alone. 



— 2. Do. and free sugar. — 5. Do. and free sugar. 



— 3. Do. and free potash. — 6. Do. and free potash. 

 In the open tubes, No. 1 did not form any protoxide until 



it had stood a week, when a slight deposition, accompanied by 

 carbonate of lime, took place ; No. c 2 formed protoxide after 

 twelve hours, and gradually increased it; whilst No. 3 did not 

 form any for a month, when a trace appeared, and at the same 

 time crystals of carbonate of lime. But in the closed tubes, 

 after twelve hours' standing, protoxide had formed in all; that 

 in Nos. 4 and 6 was slight, whilst that in No. 5 was consider- 

 able. Carbonate of lime did not appear until they had stood 

 a week. 



In order to ascertain the exact action of sugar on the oxide 

 of copper, a portion of the hydrate having been agitated with 

 a syrup in the cold for three days without any effect was 

 brought to boil, and though none was dissolved, yet the hydrate 

 was prevented parting with its water and becoming brown as 

 in ordinary cases ; and continuing the boiling the peroxide 

 was slowly converted to the yellow one, the change being 

 complete after some hours ; and the sugar, though having 

 thus partially deoxidized the copper, appears in proximate 

 properties to have itself suffered no change. If prior to the 

 boiling the smallest quantity of potash or other alkali had 

 been added, a part of the hydrate would have been imme- 

 diately dissolved, acted on by the free sugar present, and pre- 

 cipitated as protoxide, the alkaline saccharate then renewing 



