90 Account of an Apparatus for ascertaining 



have taken the principle of its formation from the paper of 

 M. Decroizelle, in the Annales de Chimie. 



I am, Sir, 



Respectfully yours, 



W. G. Colchester. 

 London, Aug. 28, 1829. 



The apparatus consists of a glass jar about one inch in dia- 

 meter, containing about five cubic inches, and graduated into 

 inches and tenths ; a dropping tube about seven or eight 

 inches long, divided into thirty equal parts ; a porcelain mor- 

 tar and pestle ; a weight of 100 grains, and a bottle of sul- 

 phuric acid, so diluted that the quantity contained in twenty- 

 two divisions of the dropping tube will just saturate fifty grains 

 of crystallized sub-carbonate of soda. To determine the 

 point of saturation litmus paper may be used, or, what is much 

 more convenient, infusion of cabbage. 



METHOD OF USE. 



The sample to be examined having been pounded sufficiently 

 to pass through a coarse sieve, rub up some of it in the porce- 

 lain mortar until it be reduced to a very fine powder ; from 

 this weigh 100 grains and return it into the mortar; add 

 thereto boiling water, a small quantity at a time, and continue 

 to rub it as long as any grittiness appears under the pestle ; 

 suffer it to stand a short time, and pour off the liquid into a 

 pint or half-pint vessel with a lip ; add more boiling water to 

 what remains, and again use the pestle, repeating this to ensure 

 the perfect solution of all the soluble part of the sample, until 

 about half a pint of boiling water has been employed ; transfer 

 the whole into the same vessel, stir it well together, and allow 

 it to stand for the insoluble part to subside; when this is 

 effected, measure off the clear liquor by pouring it into the 

 graduated jar and set it by for use; measure also the remain- 

 der, first shaking it up, and having noted the total quantity, 

 this remainder may be thrown away. Take of the clear solu- 

 tion just one half of the whole amount of the two quantities, 

 and add thereto about a table-spoonful of the infusion of cab- 

 bage ; then, having filled the dropping tube to the upper 



