end on the NatuYe of SnoW. 253 



I was now enabled to proceed a ftep further, and to deter- 

 iTiine whether after this procefs any of the bafes of air, and, 

 m particular, free oxygen, remained in the water, which 

 dunng freezing might' &e extricated in the ftate of elaftic air. 



On one of the coldelt evenings of the month of December 

 j8oi, r filled fomeflafks, in the manner already mentioned, 

 with blue-coloured water freed from its air and with nitrous 

 gas, and others with water w ithout any addition ; all of which 

 I placed in the window. Next morning no change was to 

 be obferved, though the frod had been very ftrong : "^he water 

 in all the flafks was in a Hate of perfeft fluidity. This phte- 

 nomenon, I acknowledge, is very common : but I mentioa 

 it becaufe fome confidcr the impeded difengagement of air 

 as the caufe of it ; an idea which I was not ignorant of, and 

 which agrees with the refult of this experiment. 



This circumftaiice rendered the experiment more agreea- 

 ble; and being certain that every thing would freeze on the 

 leaft agitation, I was enabled to obferve better the fmallell 

 change which would take place during the procefs of freezino-. 



What I expeded took place; none of thofc prefent duritftr 

 the freezing could oblerve the leafl change of colour. We 

 every where faw bubbles appear, and difperfe themfelves 

 widely through the lump of ice; but they were merely ni- 

 trous gas. At the end of two days we did not perceive the 

 leaft trace of rednels in the ice, till the flafk at length burft- 

 ing, and the air thus having free accefs, the whole mafs in- 

 ftantly became red. The fliilks which contained no nitrous 

 gas, or tincture of litmus, exhibited durins: the freezino- of the 

 water no air-bubbles; but when the flafe burft in^confe- 

 quence of the froft increafing, the mafs of ice was immedi- 

 ately interfperfcd here and there with air-bubbles. 



But though thcfe experiments k\\\y proved my idea in re- 

 gard to the origin of air-bubbles in ice, 1 was very defirou3 

 to obierve the pha:-nomena of freezing in vacuo. 



My fornu-r pupil and worthy friend^'an In En Kniphuifen, 

 lord of Nicnoord, who has added fo much luftrc to his noble 

 birth by an adiduous cultivation of the fciences, was fo kind 

 as to adill nie in thel'e experiments, and to allow me the ufe 

 of his valiial)le appar.itus. 



The experiment of Lichtenberg fills to the ground. We 

 have feen curious |ihapu(jmena. f iliall give you an account 

 of them, which I lind in my memorandum's, dated Janu- 

 ary 0, 1802. This will he more than liit!icient to induce 

 all the amateurs of the lludy of nature to repeal my experi- 



We had already obferved fcvcral times, with great fatisfac- 

 • ■ ' '/ tion, 



