310 Mr. Faraday on the 



as lignine, sugar, &c. ; and was surprised to find that ammo- 

 nia was still a result of the experiment. This led to trials 

 with different vegetable substances, such as the proximate 

 principles, acids, salts, &c., all of which yielded ammonia in 

 greater or smaller quantity ; and, ultimately, it was found 

 that even several metals when treated in the same way gave 

 similar results ; a circumstance which appeared considerably 

 to simplify the experiment. 



The experiment may be made in its simplest form in the 

 following manner : Put a small piece of clean zinc foil into a 

 class tube closed at one end, and about one-fourth of an" inch 

 in diameter ; drop a piece of potash into the tube over the zinc ; 

 introduce a slip of turmeric paper slightly moistened at the 

 extremity with pure water, retaining it in the tube in such a 

 position that the wetted portion may be about two inches from 

 the potash ; then holding the tube in an inclined position, ap- 

 ply the flame of a spirit lamp, so as to melt the potash, that it 

 may run down upon the zinc, and heat the two whilst in 

 contact, taking care not to cause such ebullition as to drive up 

 the potash : in a second or two, the turmeric paper will be 

 reddened at the moistened extremity, provided that part of the 

 tube has not been heated. On removing the turmeric paper 

 and laying the reddened portion upon the hot part of the tube, 

 the origiiial yellow tint will be restored : from which it may 

 be concluded that ammonia has been formed ; a result con- 

 firmed by other modes of examination to be hereafter mentioned. 



The first source of nitrogen which suggested itself was the 

 atmosphere : the experiment was therefore repeated, very care- 

 fully, in hydrogen gas, but the same results were obtained. 



The next opinion entertained was, that the potash might 

 have been touched accidentally by animal or other substances, 

 which had adhered to it in sufficient quantity to produce the 

 ammonia : the alkali was therefore heated red hot, as a prepa- 

 ratory step, and afterwards allowed to touch nothing but clean 

 glass or metals ; but still the same effects were produced. 

 The zinc used was selected from a compact piece of foil, was 

 well rubbed with tow dipped in alkali, washed in alkaline so- 

 lution, afterwards boiled repeatedly in distilled watei*, and 

 dried, not by wiping, but in a hot atmosphere ; and yet the 

 same products were obtained. 



All these precautions, with regard to impurity from finger- 

 ing, were found to be essentially requisite, in consequence of 

 the delicacy of the means afforded by heat and turmeric jiaper 

 for testing the presence of ammonia, or rather, of matter con- 

 taining its elements. As a proof of this, it may be mentioned, 

 that some seu sand was heated red hot for half an hour in a 



crucible 



