Intelligence and Miscellaneous Articles. 399 



With a pair of metallic elements, consisting of one bismuth and 

 one antimony, weighing each five grains and measuring 0*5 of an 

 inch long and 12 diameter, when their extremities were unequally 

 heated, I have obtained, with a Henry's flat ribbon coil, a very per- 

 ceptible and brilliant spark. 



I have had the pleasure of showing the experiment to MM. De 

 la Rive, Plateau, and Netschayef, and I need not add that these 

 distinguished philosophers were much delighted on seeing the ther- 

 mo-electrical light developed by a single pair of metallic elements. 



Now I have pen in hand permit me to state that with thermo-piles 

 I actuate most of the apparatus usually employed for illustrating 

 electro-magnetic phenomena, so that the public teacher may now 

 show by the same apparatus the several rotations, &c. with thermo- 

 electricity, as he does with voltaic electricity. 



I remain, Gentlemen, &c. Francis Watkins. 



5, Charing Cross. 



ON THE ARTIFICIAL PREPARATION OF FORMIC ACID. 



Prof. J. B. Emmet of the University of Virginia makes the fol- 

 lowing observations respecting, and proposes the annexed methods 

 of preparing formic acid : 



One part of tartaric acid (or sugar), one and a half of peroxide 

 of manganese, one and a half of sulphuric acid, diluted with about 

 two and a half parts of water, when well mixed and subjected to 

 distillation, will furnish the formic acid according to Dcebereiner's 

 process. In order to diminish the inconvenience arising from the 

 frothing of this mixture, and which is exceedingly great, it is directed 

 to add only half the amount of dilute acid at first, and to make use 

 of a retort having five or six times the bulk of the matter to be put 

 into it. 



The explanation given by Dcebereiner and other chemists, assigns 

 to the peroxide of manganese an agency absolutely necessary for suc- 

 cess, viz. that, while it parts with a portion of its own oxygen and 

 combines, as the protoxide, with sulphuric acid, it is enabled by the 

 oxygen thus detached, to convert the tartaric acid (or sugar) into 

 the formic and carbonic acids. 



The whole of this explanation is, however, incorrect, as will ap- 

 pear from the following results of my inquiry. 



1. The presence of peroxide of manganese, (or any other per- 

 oxide,) is not only unnecessary, but positively injurious and produc- 

 tive of much inconvenience, his positively injurious in consequence 

 of the power which all peroxides have of decomposing formic acid, 

 and productive of inconvenience in consequence of the vast amount 

 of carbonic acid which it produces with the formic acid and the car- 

 bon deposited during the operation. The latter is, in fact, the cause 

 of the excessive frothing. 



2. Sulphuric acid is not essential. The formic acid was prepared 

 by phosphoric acid as well as by the chloride of tin ; and no doubt 

 all other substances, capable of converting alcohol into aether, may 

 be shown to possess the same power. In no case does sulphuric acid, 



