VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 433 



covery he has suffered no winter to elapse without making similar experiments, 

 and never failed of success in freezing the quicksilver, whenever there was a 

 proper degree of natural cold, which he states at — 10°, in order for the experi- 

 ment to be complete, though some commencement of congelation might be 

 perceived when the temperature of the air is as high as -f- 1°. He confirms all 

 his former observations, and adds many others to illustrate them ; among which 

 two are very important, as coming nearer than any yet known to ascertain the 

 real contraction that quicksilver suffers in becoming solid. At the same time it 

 must be confessed, he has not rectified any of his former mistakes : he retains 

 the same groundless opinions relative to the freezing point of the quicksilver, 

 the prodigious cold generated by his mixtures, and the explanation of various 

 phenomena, which depend on very different principles, from those to which he 

 assigns them. 



The general state of M. Braun's experiments is, that with the above-mentioned 

 frigorific mixtures, and once, when the natural cold was at — 28°, with rectified 

 spirits and snow, he congealed the quicksilver, and discovered most, of its pro- 

 perties in a solid state, especially that it is a real metal, which melts with a very 

 small degree of heat. But not perceiving the necessary consequence of its great 

 contraction in freezing, 1 hough aware of the fact, he perpetually confounded 

 the diminution of its volume from this cause with that which is simply the effect 

 of cold. Hence he considered, as the commencement of congelation, what was, 

 in reality, its extreme term, or the utmost contraction which the whole would 

 suffer in becoming solid. To this, indeed, he scarcely ever attained, owing to 

 the various impediments that occurred from adhesion of the quicksilver in the 

 thermometrical tube, hollows left in the bulb as it froze, portions of the mer- 

 cury remaining uncongealed, and many other causes. In his supplementary 

 treatise, the professor engages to continue his researches, and to lay the result 

 of them before the academy, if they should lead to any thing new. But he did 

 not live to accomplish his design, as he died the year following. 



It was not till the year 1774, that Mr. Braun's assertions received any sort of 

 confirmation out of Russia, and then by a mode of experiment which did not 

 seem to promise much success. M. J. F. Blumenbach, then a student of 

 physic, and afterwards professor of medicine, at Gottenburg, observing the in- 

 tense cold that prevailed there in January that year, took the opportunity of ex- 

 posing some quicksilver to its action. On the 11th of Jan. M. Blumenbach, " at 

 half after 5 in the evening, put 3 drams of quicksilver in a small sugar-glass, and 

 covered it with a mixture of equal parts of snow and Egyptian sal ammoniac. 

 This mixture was put loose into the glass, so that the quicksilver lay perfectly 

 free, being only covered by it as with pieces of ice ; the whole, together with 

 the glass, weighed somewhat above an ounce. He hung it out at a window 3 



vol xv. 3 K 



