ATTRACTION, [y 



9. Galvanic Electricity, is one of the most important of these 

 causes. Its general powers have been already sketched, and it will 

 be more fully developed in the sequel. 



(HH.) LIMITATIONS OF COMBINATION. 



1. Unlimited on both sides. Water and alcohol, and water and 

 the strong acids are examples ; the smallest quantity of the one may 

 be combined with the largest of the other, and the reverse ; a drop 

 of water with an ocean of alcohol ; a drop of alcohol with an ocean 

 of water. 



2. Limited on one side. In the case of water and saline sub- 

 stances, the smallest portion of salt may combine with the largest 

 quantity of water, but if we continue to add the salt, the water be- 

 comes saturated, and any additional quantity will remain on the bot- 

 tom undissolved. Alcohol with camphor and resins, is governed by 

 a similar law. 



3. Limited on both sides to one proportion. Hydrogen gas 3 vol- 

 umes, and nitrogen gas 1 , unite to form ammonia. Chlorine gas and 

 hydrogen gas, in equal volumes, form muriatic acid. 



4. Limited to one of several proportions. Nitrogen and oxygen 

 unite in the several proportions to form nitrous oxide, nitric oxide, 

 and the nitrous and nitric acids. 



Hydrogen 2 volumes + oxygen 1, form water. 



Hydrogen 2 " " 2, form deutoxide of hydrogen. 



(I I.) THE PROPORTIONS IN WHICH BODIES COMBINE ARE GOV- 

 ERNED BY FIXED LAWS. 



Before proceeding to illustrate this proposition, we must observe, 

 that there is a vast variety in different cases, in the force of chemical 

 attraction. Sulphate of barytes is hardly decomposed by any single 

 agent, and other bodies of whose compound character we cannot 

 doubt, as fluoric acid, have not been decomposed at all ; because 

 the force of affinity is so strong between their principles, that nothing 

 has been able hitherto to overcome it. But in other cases, the affin- 

 ity is so slight that it is subverted by small variations of temperature, 

 or by very feeble attractions ; as when alcohol is separated from wa- 

 ter by distillation, or salts crystallized by the simple cooling of their 

 saturated solutions ; so, alcohol holding camphor in solution, gives it 

 up readily when water is introduced, which attracts the alcohol. 



(kk.) Properties of simple solutions, and of other feeble combina- 

 tions. The properties are, not at all, or but little changed, and often 

 in no other way, than to produce modified qualities, depending on 

 those of the parent substances, and on their proportions. Solutions of 

 gum, sugar, salts, and acids in water ; and of resins, essential oils and 

 camphor in alcohol are familiar examples. Such cases resemble 

 mixtures, in as much as there is little or no change in the properties 

 of the principles ; and we readily perceive, either by our senses or by 



