of Arsenic Jrovi other Substances. S3S 



this apparatus, a great quantity of froth is thrown up into the 

 tube, which may cause a httle embarrassment by choking the 

 jet. I have found this effect to take place most with the con- 

 tents of the stomach, with wine, porter, tea, coffee, or soup, and, 

 indeed, with all mucilaginous and albuminous mixtures. The 

 means I adopt to prevent this effect from taking place, or, at 

 least, for checking it in a great measure, is to grease or oil the 

 interior of the short limb of the apparatus before introducing 

 the substance to be examined, or to put a few drops of alcohol 

 or sweet-oil on its surface previously to introducing the stop- 

 cock and its appendages. I have, however, found, if the tube 

 be ever so full of froth in the first instance, that, in an hour or 

 two, if left ta itself, the bubbles burst, and the interior of the 

 tube becomes clear, without at all affecting the results. 



In cases where only a small quantity of the matter to be 

 examined can be obtained, I have found a great convenience 

 in using the small glass bucket g. Under such circum- 

 stances, the bent glass tube may be filled up to within an inch 

 of the short end with common water, so as to allow room for the 

 glass bucket, whicli must be attached to the cork, &c. by means 

 of a little platina wire ; a bit or two of zinc is to be dropped into 

 the bucket, with a small portion of the matter to be examined, 

 and three or four drops of diluted sulphuric acid (acid 2, water 

 14) ; and the whole is then to be introduced into the mouth of 

 the short limb of the tube. The production of gas under this 

 arrangement is much slower, and, of course, requires more time 

 to fill the tube, than in the former case ; but the mode of ope- 

 rating is precisely the same. Indeed, it is of great advantage, 

 when the quantity of arsenic present is very minute, not to al- 

 low the hydrogen to be evolved too quickly, in order to give it 

 time to take up the arsenic. 



A slender glass funnel will be found of service when as much 

 as a table-spoonful, or even a tea-spoonful of matter, can be ob- 

 tained for examination. In this case, the tube is to be partly 

 filled with common water, leaving a sufficient space for the sub- 

 stance to be examined ; a piece of zinc is to be suspended from 

 thejcork by a thread or wire, so as to hang in the axis of the 

 tube ; and the fluid to be operated on, having previously been 

 mixed|with dilute sulphuric acid, is then to be poured through 



