VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 435 



sufficiently hardened to constitute a solid coat, and then letting out the internal 

 fluid part, so as to leave a hollow in the middle. This cavity is found every 

 where beset with metallic crystals, scarcely yielding in beauty and regularity to 

 the finest configurations of salts. In like manner, with regard to quicksilver, 

 Professor Braun himself observed, that whenever it had congealed but imper- 

 fectly, and the fluid part was poured off", the solid surface which came in view 

 was extremely rough, as if composed of many small globules. One of Mr. 

 Hutchins's late observations exceedingly illustrates this matter ; for he remarks, 

 that when the fluid mercury was decanted off", in his 10th experiment. " the in- 

 ternal surface of the frozen quicksilver showed very uneven, with many radii 

 going across, some of which had heads resembling pins." Now in Professor 

 Blumenbach's experiments, the quicksilver lying loose, except the flat side that 

 touched the glass, could crystallize without impediment, and hence assumed a 

 rough, and consequently a dead white surface ; whereas in those made by Mr. 

 Braun, with tubes and thermometers, the metal being so much confined by the 

 smooth glass, its surface was rendered of a high polish, not distinguishable in 

 point of splendour from that of fluid mercury. Perhaps also, M. Blumenbach's 

 quicksilver might have been made to look duller by some dirt or moisture col 

 lected on it from the sal ammoniac and snow. 



In Jan. and Feb. 1775, Mr. Hutchins twice froze quicksilver at Albany Fort, 

 Hudson's Bay ; and in the first of these experiments, having broken his thermo- 

 meter, he found that the metal flattened by a fall of about 6 inches, bore to be 

 hammered, gave a dull sound like lead, and was finely polished on the surface. 

 The account of these experiments was published in the Philos. Trans, vol. 66. As 

 Mr. Hutchins adopted exactly the method of Professor Braun, he observed the 

 same phenomena, encountered the same difficulties from the sticking of the 

 quicksilver in the tube, and cracking of his thermometer, and was equally at a 

 loss with regard to the point of congelation. Still, however, this was the fullest 

 confirmation that M. Braun's Dissertations had ever yet received ; and it may be 

 considered as a prelude, by which Mr. Hutchins acquired the experience that 

 enabled him to succeed so perfectly in his last most decisive and satisfactory ex- 

 periments, viz. at the same place in the year 1781, as published in the Philos. 

 Trans, of the year 1783, and in the present volume of these Aridgments. The 

 preceding experiments had done little more than prove that quicksilver might be 

 rendered solid by cold, and show what sort of substance it was in that state. No- 

 thing satisfactory had been ascertained with regard to its freezing point, or the 

 degree of a thermometer at which it ceases to be a melted and becomes a solid 

 metal. It must not be supposed however, that the gentlemen who were engaged 

 in these researches neglected such a principal object of inquiry ; on the contrary, 



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