A F F

A F F

( 14 )

a red-heat, and afterwards let the gas be ex-pelled from it in the same apparatus, and it willbe found to occupy exactly the same space asthat obtained from the two grains of crystallizedsalt in the former experiment.

The same results are obtained from thesuper-carbonat and the sub-carbonat of soda.

Super-sulphat of potash in like manner con-tains twice the quantity of acid as the neutralsulphat. Let twenty grains of carbonat of pot-ash be mixed with about twenty-five grains ofsulphuric acid in a covered platina crucible, orin a glass tube, and this mixture graduallyheated till it ceases to boil and becomes slightlyred-hot. This will produce the super-sulphatof potash, which will be very nearly neutralizedby an addition of 20 grains of the same car-bonat of potash.

The common super-oxalat of potash is shewnby Dr. Thomson to consist of potash united totwice the quantity of oxalic acid necessary tosaturate it. If two equal portions of this super-oxalat be taken, and one portion calcined so asto destroy the acid, the alkali that remains willbe just sufficient to saturate the other portion.

When nitric or muriatic acid is added to thecommon super-oxalat of potash, the latter saltis only partially decomposed, and crystals formin the mixture which are found on examinationto be a Quadroxalat of Potash, or potashwith four times as much acid as will saturate it.

The formation of these various salts with adefinite excess of acid which is expressed by asimple multiple of the least definite quantity isparticularly important as it affords an answer tothe powerful objection urged by M. Bertholletagainst the common opinion of chemical affi-nity. This eminent chemist shews that a con-siderable excess of a weaker acid will decomposea compound of abase and a stronger acid j forexample, that a large quantity of nitric acidadded to sulphat of potash will occasion somec-rystals of nitre to form, though the nitric acidhas a weaker affinity to potash than the sul-phuric. But though there is an undoubted de-composition of some portion of the sulphat of

potash in this case, it is highly probable thatfor every particle of nitre formed there is anequivalent quantity of a super-sulphat of potashproduced, in equally definite proportions withthe neutral sulphat, and in which probably theacid is in the ratio of a simple multiple of thatwhich exists in the neutral salt.

Among the philosophers who within theselast few years have laboured with the greatestzeal and success in discovering the laws ofchemical affinity a distinguished place is due toProfessor Berzelius , c whose experiments weshall now briefly notice. He states that he wasled to this train of enquiry from the two follow-ing most important theorems laid down by thelearned Richter.

I. When two bodies A. and B. have each anaffinity for two others C.and D. the C. whichsaturates a given quantity of A. is to the D.which saturates the same quantity of A. in thesame proportion as the C. saturating any givenquantity of B. is to the D. saturating the samequantity of B. Hence the saturating propor-tions of A. C. A. D. and B. C. being knownthote of B. D. may be found by simple calcula-tion. For example, let A. B. C. and D. berespectively sulphuric acid, muriatic acid, ba-rytes and potash, and let 100 parts of sulphuricacid be saturated by 190 of barytes, and by J W ofpotash, and let 100 of muriatic acid be saturatedby 281 of barytes, then, the quantity of potashsaturating 100 of muriatic acid will be 173;

Bar. Pot. Bar. Pot.for 190 : 116 : : 2S1 : 173 nearly.This law of chemical combination is indeed adirect inference from the fact that when twoneutral salts are mixed together and decomposeeach other the mixture remains neutral. Tims,supposing 381 parts of muriat of barytes beexactly decomposed by 322 parts of sulphat ofpotash, and the mixture remain neutral, the re-spective proportions of the new compoundsformed will be 273 of muriat of potash, and430 of sulphat of barytes, as by the followingscheme:

381

1

1 Si

I f:

100 _

281

l r

ji •

273

Muriatic Acid

Barytes.

4 SO

i ;

Muriat of

<

Sulphat of

]! 1 '

Potash.

173

149

Barytes,

Potash "\322Sulphuric Acid.

• An- Chjm. Tom. 77 to 83 inclusive.

J,