CORRIGENDA ET ADDENDA. 607 



material in each solution as will be sufficient to make tlio 

 two solutions, when mixed together, of about the same 

 density as that of the nascent carbonate of lime, and 

 a state of perfect rest of the fluid in which the decomposi- 

 tion is going on, so that the newly-formed compound may 

 be interfered with as little as possible in its subsidence to 

 the sides and bottom of the vessel. This will require two 

 or three weeks, or longer, according to the size and com- 

 pleteness of the calculi. But I have not found that they 

 increase at all after six weeks. 



" The specific gravity of the compound solution should 

 be 1*4068, when one ounce will weigh 672 grains. This 

 solution must be perfectly clear ; all the carbonate of lime 

 which had been formed by the decomposition of the 

 malate of lime contained in the gum, and also all the 

 triple phosphate set free by the alkali, must have been 

 allowed completely to subside. Next, two clean micro- 

 scopic slides of glass, of the ordinary dimensions, are to be 

 introduced, with the upper end of one slide resting against 

 that of the other, and with their lower ends separate as 

 far as the width of the phial will permit ; and lastly, the 

 bottle is to be filled up with a solution of gum arabic in 

 common water, of 1-0844: specific gravity, one fluid ounce 

 of which will weigh 520 grains. This solution must also 

 be perfectly clear, having been first strained through 

 cloth, and then left to stand for some days to allow of the 

 subsidence of all the floating vegetable matter. It must 

 also be added carefully to the alkaline solution, that the 

 two solutions may be mixed as little as possible in this 

 part of the process. The bottle must now be kept per- 

 fectly still, covered with a piece of paper to prevent the 

 admission of dust, for three weeks or a month. Time 

 would be saved by having a dozen bottles thus charged, 

 and examining their contents at stated intervals, according 

 to the chief object sought for in the experiment. The 

 soluble salts of lime to be decomposed by the sub-carbonate 

 of potash are contained in the gum, in combination with 

 malic acid, and also in the common water; ammoniaco- 

 magnesian or triple phosphate is also contained in the 

 gum, and is set free by the alkali. Muriate of lime, dis- 

 solved iu a solution of gum from which all the lime had 



