J04. , Ohfeivai'isiis and Expcrinunts on 



A mixture made of diluted nitrous acid, phofphorated foda, and nitrous ammoniac, (by 

 much the mod powerful of any compounded of falls with acids,) prepared with thegrcateft 

 accuracy, is not quite equal to a mixture of fnow and nitrous acid, each mixed at -(- 30 

 degrees, although very nearly fo. 



Though quickfilver may be frozen by falts diflblvcd in acids, it is necefTary that the ma- 

 terials be cooled prcvioufly to mixing, much lower than when fnow or ground ice are 

 ufed. 



If it be required to mix the powdered falts and acids at a low temperature, the bcft me- 

 thod is this :— Put firil the nitrous ammoniac into the tube of fuch an apparatus as fig. i, 

 fhaking it down level, gently prefTing the upper furface fmooth; then the phofphorated foda 

 or Glauber's fait : cover this with a circular piece of writing paper, and pour a little melted 

 M-hite wax upon it, and when cold pour upon this the diluted nitrous acid: immerfc this 

 in a frigorific mixture till it is fufRciemly cold, a« found by dipping the thermometer into 

 the liquor occafionally ; force a communication through, and ftir the whole thoroughly to- 

 gether, contriving that the upper ftratum of fait, that is, the phofphorated foda or Glauber's 

 fait, be mixed with the liquor lirft, and then the nitrous ammoniac ; the powdered falts do 

 not require ftirring whilft cooling, like fnow, for, however hard they are frozen, they will 

 readily diflblve in tl>e acid : care mud be taken that the partition be perfect between the 

 falts and the liquor, and that in this and every inftance where the materials are to be cooled 

 they be immerfed below the furface of the frigorific mixture. The ftrength of the red fum- 

 ing nitrous acid ufed in thefe experiments 1 found to be 1,510, and that of the vitriolic 

 acid 1,848. 



I have thought it better, for the fake of brevity, not to ufe in this, as in my former papers, 

 the new chemical names, efpecially as the old ones are more generally known. 



Thefe experiments were chiefly made in a warm room, not far from the fire-fide. 



I have now finirtied my propofed plan refpe(fling the bed modes of condu£ling experi- 

 ments on cold ; in which it will appear, that I have reduced the congelation of quickfilver, 

 in any climate, at any feafon, to a certain and almoft as eafy a procefs as that I originally 

 fet out with for the freezing of water, (Phil. Tranf. vol. lxxvii.) viz. by previoufly cooling 

 the materials in one mixture, to produce the effeft in a fecond. It may very likely appear 

 to fome, that I have been too minute in a few particulars; yet, as perhaps experiments of 

 this kind, all circumftances confidered, are inferior to few in the delicacy required to make 

 them fucceed completely, I truft I fhall be excufed by thofe who choofe to repeat them, 

 particularly fuch as are not in the habit of making experiments of this kind — efpecially if 

 it fecure them from an unfuccefsful attempt, and that perhaps without being able to account 

 for it. 



Oxford, March 1, 1795. 



It is very well known, that vitriolic ether will produce fufficlent cold by evaporation to 

 freeze water. This circumftance is noticed by many ; and feveral different methods have 

 been propofed, particularly one by Mr. Cavallo, with a very ingenious apparatus for the 

 purpofe (Phil. Tranf. vol. Lxxi.) ; nevcrthclefs, as I am upon the fame fubjcft, and tlie 

 following experiments differ, as well in the tfttGt produced, as in the particular mode of 

 condufluig them, from an^ I have met with, I have ventured to mention them. 



June 



