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An important benzaldehyde-test is that for the presence of chlorine- 

 compounds, and for this reason it has been incorporated in the new Edition 

 of the German Pharmacopoeia among the tests prescribed for this article. 

 The Pharmacopoeia reference is as follows (p. 73): "When a small piece 

 of folded filtering-paper is saturated with 1 g. benzaldehyde, burnt in a 

 porcelain dish under a large glass beaker, the inside of which has been 

 moistened with water, and the contents of the beaker, after combustion, 

 are rinsed out with a little water and poured on a filter, the filtrate, when 

 acidulated with nitric acid, must remain clear upon the addition of a silver 

 nitrate solution". 



This method has been criticised by J. Herzog 1 ) at the March 

 meeting of the German Pharmaceutical Society. According to Herzog's 

 experience it is very difficult to carry out the test when the method 

 of the Pharmacopoeia is adhered to closely. "The reaction", he said, 

 "will either give no result at all, or will be effective only with benzaldehydes 

 containing an abnormally large proportion of chlorine". Herzog found 

 that an addition of 5 drops chlorobenzene to 5 g. benzaldehyde only 

 gave the faintest possible chlorine reaction when the test was carried out 

 in accordance with the Pharmacopoeia requirements, and that an addition 

 of only 2 drops of chlorobenzene to 5 g. benzaldehyde could not be 

 detected at all by this method. His explanation of the non-reaction is 

 that complete combustion of the paper soaked in 1 g. benzaldehyde makes 

 the beaker so hot that the water adhering to its sides, and with it any 

 hydrochloric acid which may have been absorbed, is eventually completely 

 evaporated, and that the hydrochloric acid is thus lost for the purposes of 

 identification. In order to obviate this trouble Herzog recommends that 

 instead of 1 g. only 0,2 g. benzaldehyde (he himself uses 4 drops) be burnt 

 each time, for when this is done the beaker is not overheated and its 

 contents remain moist. With the two mixtures referred to above Herzog 

 obtained a heavy precipitate in one case, and a noticeable precipitation 

 of silver chloride in the other. 



As we also feel ourselves entitled to express an opinion on the sub- 

 ject of the chlorine test for benzaldehyde, we wish to point out that we 

 are unable to endorse Herzog's proposal without reservation, because 

 when such a small quantity of benzaldehyde is used as is recommended 

 by Herzog, the limit of sensitiveness of the reaction is also reduced. 

 And this is a most material consideration, for in most examinations the 

 question at stake will not be whether the benzaldehyde contains a greater 

 or smaller proportion of chlorine but, whether or not it contains traceable 

 proportions of chlorine at all. Therefore, when following Herzog's 

 advice and using only 0,2 g. aldehyde, a benzaldehyde may in cer- 

 tain circumstances be pronounced to be chlorine-free which when tested 



2 ) From the Report of the Meeting in the Berichte d. deutsch. pharm. Ges. 21 (1911), 202. 



