Perhaps all liquids should be considered as _pure_ that are subject to uniform congelation at certain temperatures on the one hand, and on the other are capable of being distilled by heat without any alteration in their constitution. Water and mercury will rank in the first place; alcohol of .82 specific gravity and ether of .72; concentrated sulphuric acid; nitric acid of 1.42 specific gravity: naphtha and oil of turpentine, &c. will probably be thought to claim the next place. It is desirable that the temperatures at which these liquids congeal should be ascertained; also whether any decomposition is effected by the operation. If these expand proportionally to a scale of square numbers for certain given equal or unequal intervals of temperature, it may point out something relative to the collocation of the ultimate particles in liquids. The apparent coincidence of this rate of expansion in liquids, with the geometrical progressive force of steams or vapours creates an additional interest. It may be that most or all of these supposed relations are accidental, and only approximative like that of the rate of expansion of air and mercury, between the temperatures of -40° and 212°; but I cannot think this probable. Even should they be only approximations, they are of sufficient utility to be kept in view. _FINIS._ _Printed by the Executors of S. Russell_ BOOKS, ESSAYS, &c., _PUBLISHED BY THE SAME AUTHOR._ METEOROLOGICAL OBSERVATIONS AND ESSAYS. 4_s._ 8vo. 1793. ELEMENTS OF ENGLISH GRAMMAR: or, a new System of Grammatical Instruction, for the use of Schools and Academies. 2_s._ 6_d._ 12mo. 1801. ☞_A few Copies of these Works may still be had of the London Booksellers._ A NEW SYSTEM OF CHEMICAL PHILOSOPHY. Part I. of Vol. I. 7_s._ 8vo. 1808. Published by G. Wilson, Bookseller, Essex Street, Strand, London. _ESSAYS, by the same, in the Memoirs of the Literary and Philosophical Society, Manchester._ VOL. 5. PART 1.--Extraordinary facts relating to the vision of colours. PART 2.--Experiments and observations to determine whether the quantity of rain and dew is equal to the quantity of water carried off by the rivers, and raised by evaporation; with an enquiry into the origin of springs. Experiments and observations on the power of fluids, to conduct heat, with reference to Count Rumford’s seventh essay on the same subject. Experiments and observations on the heat and cold produced by the mechanical condensation and rarefaction of air. Experimental essays on the constitution of mixed gases; on the force of steam or vapour from water and other liquids, in different temperatures, both in a Torricellian vacuum, and in air; on evaporation; and on the expansion of gases by heat.