New Experiments upon Ice; Taken from Abbé Nolet, F. R. S. at Paris, and Communicated by J. T. Desaguliers, F. R. S.

II. New Experiments upon Ice; taken from Abbé Nolet, F. R. S. at Paris, and communicated by J. T. Desaguliers, F. R. S. 1. Ice that begins to melt, and Water that begins to freeze, have always the same Degree of Cold. 2. That Cold may be increas'd by a Mixture of Salts. 3. It has been thought for a long time, that Salt-petre was most fit to increase the Cold of Ice; but Experiments have shewn, that few Salts increase Cold so little as that Salt. Mix one Part of fine Salt-petre with two Parts of beaten Ice, and Mons. Reaumur's Thermometer will descend in it but $3\frac{1}{2}$ Degrees below the freezing Point. What had caus'd this Mistake, is, that People generally made use of Salt-petre of the first or second Melting, as being the cheapest; but that Salt-petre not being purified, contains a great deal of Sea-Salt; and it was in Proportion to the Quantity of the Sea-Salt that the Effect was the greater. From this last Observation, one may deduce an advantageous Method for trying Gunpowder; for as of the three Ingredients of which it is made up, Salt-petre is the only one that can increase the Cold of Ice; if one Part of Gunpowder, or a little more, be mix'd with two Parts of Ice, and it increases its Cold more than $3\frac{1}{2}$ Degrees, it is a Sign that the Salt-petre contain'd in it is not well purified; and the best Pow- der will be that which does least increase the Cold of Ice. 4. Sea-Salt, that is the Bay-Salt, which is commonly us'd at Table in France, and that which is immediately taken from the Mines, call'd Sal gemmae, give the greatest Degree of Cold, for the most part; for Pot-ash gives sometimes a little more, but generally less. Sea-Salt mix'd with Ice in the abovesaid Proportion, gives 15 Degrees of Cold on Mons. Reaumur's Thermometer, and Sal-gem. 17. 5. Ashes of green Wood 3 Degrees. 6. of Sea-Coal 7. of Vitriol 2 8. Tartar 10 9. Common Pot-ash (in French call'd Saude ordinaire) 3 10. Pot-ash made of Vreck or Sea-weed 11 This last Pot-ash may be substituted instead of Sea-Salt, for making Ice-Creams, in Places where Salt is dear, as in France, where it is sold for 10 Sols a Pound. 1st, Because in France this Pot-ash is sold only for 2½ Sols a Pound. 2dly, Because, not freezing so fast, it does not spoil the Creams by reducing them to Icicles. 3dly, Because Ice-Creams made this way, will keep longer in a Condition fit to serve at Table. 11. Sugar . . . . . . 4 Degrees. 12. Allom . . . . . . 1½ 13. Salt of Glass . . . . 10 14. Sal 14. Sal Ammoniac . . . . 12 \( \frac{2}{3} \) Degrees. 15. Quick-Lime . . . . 1 \( \frac{1}{4} \) 16. Sal Glauberi . . . . 2 17. The Cold of Ice may still be considerably increas'd by a Mixture of Spirit of Wine; about a Drinking-glass full of Spirit of Wine to a Pound of beaten Ice. 18. The Cold of Ice will not increase, unless the Ice melts. **EXPERIMENTS.** Put into one Vessel four Ounces of Ice beaten very small, and into another Vessel two Ounces of Sea-Salt; set the two Vessels in a Mixture of Ice and Salt, which is to be renew'd still, till by means of the Thermometer you find, that the Salt and the Ice of the two first Vessels have acquir'd each of them 10 or 12 Degrees of Cold; then mix your Salt with your Ice, and this Mixture will not increase the Degree of Cold that the Ingredients had acquir'd, because the Mixture does not melt. But if instead of Salt you mix'd with your Ice Spirit of Nitre cool'd to the same Degree as the Ice, as this last is liquid, it will melt the Ice, and considerably increase its Cold. 19. Salt mix'd with Water, increases its Cold. 20. Of all Salts, Sal Ammoniac gives the greatest Degree of Cold; so that if that Salt has been cool'd in Ice, and then one Part of it be thrown into two Parts of Water cool'd to the same Degree in Ice, that Water will become colder than Ice, and will freeze other Water thrown into it in a small Quantity. This last Observation may be applied to the cooling of Liquors where no Ice is to be had; for there is hardly any Place, but what has Wells: Now the Water of a Well moderately deep, wants about eight or ten Degrees of the Cold of Ice; and Sal Ammoniac being cool'd beforehand in the Well, will, by mixing with some of the Water of that Well, come very near to the Cold of Ice. III. An Observation of the Magnetic Needle being so affected by great Cold, that it would not traverse; by Capt. Christopher Middleton, F. R. S. In a Letter which was publish'd some Years ago in the Philosophical Transactions, (N° 418.) I made Mention of a strange Phenomenon relating to the Sea-Compass, which I had frequently observed, when we were among the Ice in Hudson's Bay; to wit, that the magnetic Virtue of the Needle was so far lost or destroyed, that it would not traverse as usual, even when the Ship was in a considerable Motion: And in my Voyage thither last Year, I observed our Compass would not move at all, any longer than the Quarter-Master kept touching it. We had then much Snow on the Land, and many Isles of Ice around us, and the Sea not very smooth: I order'd one of the Compasses to be brought into the Cabin, but did not find it any better, till it had stood near the Fire about a Quarter of an Hour, and then it began to traverse very well; I then order'd it to be placed in the Binnacle,