438 On tlie Nature and Comlinallons 



deposited much more crystals than mature apples would have 

 done. 



The truth was now manifest. Beside the malic, there is an- 

 other acid formation, which in different fruits is formed at dif- 

 ferent periods, and which has hitherto escaped ohscrvation: and 

 I consider the preceding details by no means redundant, inas- 

 much as they estabish one decided difference between the two 

 acids. Many others will shortly be stated. 



The first step towards confirming the difference, was to obtain 

 the new acid in a state of purity: and after numerous attempts, 

 I found that the only way to obtain it pure, was to separate it 

 from the crystals. The process is indeed complex and difficult. 



The berries of the Surbns aucuparia are to be collected when 

 first they have arrived at maturity. After sufficient liruising in 

 a Wedgwood mortar, they are to be subjected to strong pres- 

 sure in a linen bag. If collected at the most favourable time, 

 they will afford nearly one half their weight of juice, s. G. 1077. 

 This after due subsidence is to be strained, and mixed with fil- 

 tered solution of acetate of lead. The precipitate is to be col- 

 lected on a filter, and in order to separate any uncombined co- 

 louring matter, it should be washed with ccld water. A very 

 large quantity of boiling water is to be poured on the filter, and 

 allowed to pass through the precipitate into different glass jars. 

 After some hours, the washings become opaque, and at length 

 deposit crystals of singular lustre and beauty. Those which 

 have been formed in the colourless washings are to be alone re- 

 tained; they are to be separated by the filter, dried in the air, 

 and preserved for a further process. 



The original mass remaining on the filter, from which the 

 crystals have been obtained, being now hard and brittle, is in- 

 capable of affording any more, without undergoing a new ope- 

 ration. It is to be boiled for half an hour with a little more 

 dilute sulphuric acid than is sufficient to decompose the salt ; 

 when cold it is to be filtered. The filtered liquor is to be mixed 

 a second time with acetate of lead ; the precipitate washed, as 

 before, with boiling water, and the crystals selected from the 

 colourless washings only. The remaining mass again grown 

 hard, is to undergo the process of decomposition with sulphuric 

 acid, combination with lead, and the formation of crystals : and 

 after all, it will be found that the crystals of all the processes 

 will be inconsiderable when collected. 



The whole of the crystalline product being dried, is to be 

 boiled for half an hour Avith 2*3 times its weight of sulphuric 

 acid, s. G. 1090, supplying water as fast as it evaporates, and 

 taking care to keep the mixture constantly stirred with a glass 

 rod. Tbe clear liquor is to be filtered off, and poured into a 



tall 



