Seventeenth Annual Meeting. 91 



fluor-spar and potassium bisulphate, as a blow-pipe reagent in the detection of boron 

 and the alkalies in their mineral combinations. (C. N., 49 — 269,) 



According to E. Fischer, para-amido-dimethyl-aniline sulphate is a much more deli- 

 cate test for hydrogen sulphide than either lead acetate or sodium nitro-prusside. (J. C. 

 S., CCTV—109.) 



For the detection of free sulphuric acid in vinegar, Wharton evaporates down to a 

 syrup, Ids cool to a hand-heat, and then stirs in a few centigrams of potassium chlorate. 

 If there is more than one percent, of sulphuric acid the mass ignites violently. Smaller 

 quantities are detected by the odor of chlorine. (C. N , 50 — 68.) 



R. T. Thompson has made a large number of observations on the use of litmus, 

 rosolic acid, methyl-orange, phenacetolin, and phenolphthalein as indicators. The writer 

 can only refer to the original articles. (C. N., 49 — 82, 38 and 119.) 



EXPERIMENTS UPON SUPER-HEATED LIQUIDS AND UPON THE 

 SUPER-SATURATION OF VAPORS. 



EDWARD L. NICHOLS, PH. D. 

 I. 



It is the purpose of this paper to describe some experiments upon the behavior of 

 liquids heated beyond their boiling points under conditions which prevent ebullition, 

 and of vapors cooled below the temperatures at which they ordinarily return to the liquid 

 state. , 



Professor James Thomson*, in a discussion of Andrews's f well-known experiments 

 on the continuity of the liquid and gaseous states, has shown that there are reasons for 

 thinking that under proper conditions liquids might be converted into vapor even below 

 the critical temperature without discontinuity; and he has shown the general form 

 which the curve indicating the changes of volume might be expected to take. The 

 change of state may be brought about by decrease of pressure or by increase of temper- 

 ature. The former was the method adopted by Andrews in his research upon carbonic 

 acid, and the curves given in Thomson's paper, based upon those experiments, are iso- 

 thermal curves indicating variations of volume with the pressure. All that he has said 

 on this subject is applicable, however, to methods in which the temperature is varied. 



When heat is applied to a liquid at ordinary pressures, volume and temperature vary 

 simultaneously until the boiling point is reached, when the temperature becomes con- 

 stant and the familiar expansion-curve becomes a straight line, parallel to the axis along 

 which volumes are measured. Figure 1 shows this curve (A B F G) in the case of 

 water heated at a pressure of 760 mm. We know from the experiments of DonnyJ, 

 Dufour| and others upon superheated liquids, that the curve does not always take this 

 form, since water, holding no absorbed gases and contained in perfectly clean vessels, can 

 be heated far above its boiling point without ebullition. The general form pointed out 

 by Thomson for the isothermal method, but applied to the isobaric expansion-curve, is 

 shown in the dotted line (B C D E F). The condition under which a liquid will fol- 

 low t lie limb B C D is the absence of absorbed gases. The limb FED should be ob- 

 tained by cooling a vapor in the absence of its liquid. 



*Janies Thomson; Report of the British Association for the Advancement of Science, 1871 ; also 

 Proceedings of the Royal Society, 1859 and 1871. 

 t Andrews ; Philosophical Transactions, 1869. 

 X Donuy ; Annales de Chimie, 1846, 3d series, Vol. XVI. 

 j! Dufour ; Bibliotheque Universelle, Archives 1861, Vol. XII. 



