470 Frederick Guthrie on Eutexia. 



two salts used have either a common basic, or a common acid 

 constituent. 



Thirdly, are to be eschewed those salts which attack at high 

 temperatures the vessels employed. 



Amongst all salts perhaps Nitre answers these requirements 

 best, as the body whose homologue is ice in the previous 

 memoirs of Salt-solutions and Attached Water. Nitrates do not 

 form double salts with one another, nor with other salts (com- 

 pare, however, Karsten). Nitre may be raised without suf- 

 fering decomposition to a temperature far above its temperature 

 of fusion ; possessing in this respect a wider range of available 

 temperature than nitrate of ammonium, which might otherwise 

 be preferable on account of its lower melting-point. 



§ 209. In the following paragraphs, from § 210 to § 227, 

 temperatures up to 280° C. were measured by means of a 

 mercurial thermometer. Those above that range were deter- 

 mined by an air-thermometer with a horizontal stem about 

 three feet long. The index was a plug of mercury. The 

 total range was from about 0° to 380° 0. As most of the 

 experiments in which the air-thermometer was used were 

 made on days on which the barometric pressure was nearly 

 the same, no correction was needed. On other days the air- 

 thermometer w T as standardized at the temperature of boiling 

 water, with the mercurial one placed by its side in the water. 



§ 210. Nitre. — I find that the temperature of fusion of 

 pure nitre is 320° C. 



§ 211. Nitre and Chromate of Potassium. — If nitre be fused 

 in a large porcelain crucible and neutral chromate of potas- 

 sium be added, some of the chromate is dissolved. The higher 

 the temperature the larger the quantity. On suffering the 

 solution to cool slowly, chromate of potassium separates out 

 in fine powder, which sinks through the fused mass. The 

 temperature falls till it reaches 295°, at which it remains 

 constant ; and the liquid begins to solidify. The liquid por- 

 tion is poured into a fresh crucible; and this maybe repeated 

 any number of times. The temperature of solidification is 

 constant. The liquid being poured upon a cold slab solidifies 

 to a mass, which has when cold precisely the colour of sulphur. 

 Of this alloy 2*4881 grams gave 0*1226 chromate of barium. 

 This corresponds to 0*0936 chromate of potassium, which is 

 3*76 per cent. Accordingly this alloy is: — 



Melting-point. 

 Nitre ....... 96*24 I ^ 



Chromate of potassium . 3*76 J 



§ 212. Nitre and Nitrate of Calcium. — The three metals 

 calcium, strontium, and barium promised to be of interest in 



