1:56 Scientific Intelligence. [Feb. 



5. Is there any certain method of detecting barley or potatoe 

 flour in wheaten bread? When wheaten flour is dear, bread con- 

 tains l-4th or l-5th of that frqm barley or potatoes. Now it is 

 hard to pay four-pence or five-pence for a pound of what might be 

 had for one penny in the shape of potatoes. 



Answer. The best criterions for detecting the pre^rcnce of these 

 substances is the colour, taste, and appearance of the loaf. If it 

 be hard, blacky and doughy, the presence of some improper article 

 may be pretty confidently suspected. 



fl. Of what use is lime in the smelting of iron, as stated in Dr. 

 Thomson's Travels in Sweden ? 



Answer. Lime is always used by the smelters of iron. It has 

 the property of forming a glass with the clay which is usually 

 mixed with the ore, and thus separates it from the iron. I believe 

 that, in some of our founderies, too much lime is often used. 



XII. Test for Arsenic. 



In consequence of a paragrapji in the last number of the Annals 

 of Philosophy, I have received a letter from Mi. Hume, of Lotg 

 Acre, claiming the original discovery of the application of nitrtte 

 of silver as a test of the presence of arsenic when in solution, ac- 

 companied by all the documents on which that claim is founded. 

 I have perused them, and find the following to be the facts. The 

 test was first proposed by Mr. Hume, and his description of the 

 application is sufficient to show us that he understood the principle 

 upon which it acted ; though he does not explain that principle in 

 his letter published in the Philosophical Magazine for \SW.). It 

 was easy for any chemist to apply that principle. Dr. Marcet's 

 mode of using the test I consider as an improvement, though I 

 have no doubt it was suggested by Mr. Hume's letter. As to Mr. 

 Hume's last method, I have never tried it ; but see no reason to 

 doubt that it will answer. 



Xni. Iodine. 



I have made some trials on the production of iodine, and con- 

 ceive it right to state the results that I have obtained, as it may 

 save others some needless trouble. Pounded kelp did not yield 

 any of it. When kelp is treated with water till every thing soluble 

 is taken up, the insoluble residue I found chiefly carbonate of lime. 

 It did not yield any iodine when treated with sulphuric acid ; but the 

 dry salt extracted from kelp by water yields it in abundance. My 

 method of proceeding was as follows : Take a tubulated retort, rather 

 deep, but not large, and having a short neck ; fix its beak into a 

 large globular glass receiver, (the larger the better,) leaving room 

 for the air to escape ; put the dry salt into the retort, pour strong, 

 sulphuric acid on it through the mouth of the retort, and ther^ 

 close it with a stopper. A violent effervescence ensues ; the violet 

 gas is driven off in abundance. It crystallizes upon the inside of 

 the receiver, and may be washed out with water. The water em- 



