CHEMISTRY. 



done honour to our own times, are a 

 proof of their diligence and sagacity. 



We do not know of any means of as- 

 certaining 1 , by experiment, whether com- 

 pound bodies do enter as principles into 

 other bodies still more compounded ; or 

 whether in bodies of three or more prin- 

 ciples, all the simple particles do dis- 

 pose themselves without any dependance 

 on the order of time, according to which 

 they may have been put together. It is 

 probable that the former is the case, so 

 that we may hereafter be enabled to de- 

 signate primary principles, or bodies not 

 yet decomposed ; secondary principles, 

 or bodies of two primary principles, 

 which nevertheless can enter into com- 

 bination, or be disengaged without sepa- 

 ration from each other ; ternary princi- 

 ples, &c. In this manner sulphur, by 

 combining with oxygen and water, will 

 form sulphuric acid, and this acid may be 

 combined with a metal, so as to form a 

 salt capable of giving out its acid again by 

 heat. Our systematic books are written 

 according to the supposition of seconda- 

 ry and more complicated principles ; but 

 the facts do not indisputably prove their 

 existence. 



When two bodies in the solid state 

 which are disposed to combine are brought 

 into contact, the combination will begin 

 at the place where they touch; and if the 

 compound be of such a nature, as that its 

 freezing point (see CAIORTC) is lower 

 than the common temperature of the bo- 

 dies, it will be fluid, and the combination 

 may proceed to the other parts of each, 

 till the whole shall have united. Thus 

 snow and salt will form a fluid brine, if 

 the temperature be higher than 6 be- 

 low the commencement of Fahrenheit's 

 scale. 



If a solid be united with and suspend- 

 ed in a fluid, the former is said to be 

 dissolved, or in solution, and tlie fluid is 

 called a solvent. In this manner water 

 dissolves sugar or salt. Fluids in gene- 

 ral dissolves greater quantities the higher 

 the temperature, probably from the fluid 

 state being promoted by heat. 



Some substances unite in all propor- 

 tions, such as most acids in water ; but 

 others have a limit ; as, for example, 

 water will dissolve only one-fourth of its 

 weight of common salt. It is then said to 

 be saturated. But chemists use the word 

 saturation in anothersense. When two 

 principles, as, for instance, an acid and an 

 alkali, are combined, the properties of 

 each disappear when a due proportion 

 of each is present ; but if either of the 



VOL. in. 



principles exceed that proportion, the 

 predominating property will be that of the 

 principle which is in excess In these 

 cases, the principles are said to be satu- 

 rated when the properties are most com- 

 pletely balanced ; but in the other cases; 

 the principle which is defective in quan- 

 tity is said to be super-saturated, or over 

 saturated, and the other principle which 

 is in excess, is said to be under-saturated: 

 acids united with alkalies manifest these 

 cases very strikingly. 



In the consideration of the phenomena 

 of chemical or elective attraction between 

 the principles of bodies, it will be very 

 difficult to select instances for illustra- 

 tion, which shall be simple, either as to 

 the principles or the effects, because in 

 almost every case there is a degree of com- 

 plexity which obtains in nature ; and even 

 where we suppose a great simplicity of 

 principles, they may hereafter be dis- 

 covered to be compound. But the doc- 

 trine will be understood, and fixed in 

 the memory, by the examples to be 

 brought; in the same manner as when 

 diagrams are used by geometricians-, 

 though the actual figures cannot strictly 

 agree with their hypotheses or postu- 

 lates. 



1. The mutual action of two bodies ex- 

 hibits the phenomena of simple elective 

 attraction and rejection : when two prin- 

 ciples are presented to each other, the) 

 may either combine or reject each other. 

 Thus water combines with and dissolves 

 gum, but rejects camphor ; and alcohol 

 combines with and dissolves camphor, 

 but rejects gum. 



It is probable, that all simple bodies, if 

 insulated, would combine together, and 

 that the phenomenon of rejection, when 

 it takes place, is an effect of some of the 

 compound elective attractions,uponwhich 

 we shall presently speak. 



When a body is suspended to satura- 

 tion in a solvent, no more can be taken 

 up or supported, because the cohesive 

 attraction, or that of the parts of the 

 body to each other, is stronger than 

 that of the fluid to the same; and it is 

 found that the power of the solvent i 

 greater the less it is charged, until it 

 ceases at the point of saturation. Elas- 

 ticity, or the energies by which bodies 

 are converted into gas or vapour, is like- 

 wise an opponent to solution or combina- 

 tion, and gives a point of saturation 

 which may be varied, by preventing or 

 impeding the assumption of the elastic 

 state. 



3. W r hen three bodies or principles are 

 X 



