covered with a coat of REDUCED GOLD, which remains PERMANENT.

241. If a piece of white silk be immersed in an aqueous solution of nitrate of silver, thoroughly dried in the dark, and then exposed to sulphurous acid vapours, it will suffer no change; nor, if it be wetted with alcohol and then replaced in the vapour, will any sign of reduction appear; but if it be wetted with pure water, and then exposed to the vapour, METALLIC SILVER will immediately be seen on its surface.

A glass funnel is a convenient apparatus for these experiments. The silk may be suspended by a thread passed through it, and made fast to the funnel with a cork. The funnel is then 'to be placed on a table, and by moving it a little over the edge of the table, a lighted match may be readily introduced, and when the glass is full of vapour the match may be withdrawn. The va pour is confined by sliding the funnel back upon the table; and thus the phenomena of the experiment may be easily observed.

242. Dip a piece of white calico in an aqueous solution of acetate of lead, and then drop a little solution of sulphuret of potass upon it. If this be now placed in the palm of the band, the LEAD will be observed gradually to revive, and will soon be reduced to its METALLIC STATE.

243. Dissolve some sulphuret of potass in alcohol, and immerse a slip of white silk in the solution. If a drop of an aqueous solution of sulphate of manganese be now applied, films of METALLIC MANGANESE, bright as silver, will instantly appear.

244. If a bit of silk be imunersed in diluted acetate of lead, and exposed while wet to a stream of sulphuretted hydrogen gas, a brown tinge will instantly diffuse itself, like a passing shadow, over the whole surface of the silk, accompanied with a bright coat of REDUCED LEAD, resembling silver.

245. If a piece of silk be immersed in an aqueous solution of muriate of tin, and exposed while wet to a stream of the same gas, REDUCED TIN of great brightness will imme. diately cover the surface, and in a little time this will be accompanied by various colours, such as BLUE, ORANGE, and PURPLE.

246. A piece of silk, treated in the same way, but dipped in an aqueous solution of muriate of arsenic, will be covered with resplendent METALLIC ARSENIC, attended with a CITRON YELLOW COLOUR.

247. Prepare two glasses of very dilute nitrate of copper; into one drop a little liquid ammonia, and into the other some diluted arseniate of potass. The addition of these two colourless solutions will produce very different effects; for the one glass will have an abundant precipitate of a beautiful GRASS GREEN, and the other a precipitate of a brilliant SAPPHIRE BLUE.

For the following Experiments I am indebted to the polite communication of Sir Humphry Davy, Professor of Chemistry at the Royal Institution.

248. Take a small piece of pure potash, gently breathe on its surface, and place it on an insulated plate connected with the negative side of a powerful galvanic battery in a state of intense activity. Then bring a metallic wire from the positive side of the battery in contact with the upper surface of the alkali, and soon a very vivid action will be observed. Small globules, having a high metallic lustre, and of the appearance of quicksilver, will be seen, some of which will burn with explosion and a bright flame as soon as they are formed. Thus POTASH may be DECOMPOSED AND ITS metallic BASE RENDERED VISIBLE in a separate state.

249. Take the metallic substance formed in the last experi ment, called potasium, make it very hot, and confine it in a small glass vessel of oxygen gas. Here a rapid combustion, with a brilliant white flame, will be produced, and the metallic globules will be converted into a white and solid mass, which will be found to be REGENERATED PURE POTASS.

250. Place a small piece of potasium within a dry wineglass, and in order to acquire an idea of its specific gravity pour a little alcohol, ether, or naphtha upon it: when, quitting the bottom of the glass, it will immediately rise to the surface of the liquid, it being, notwithstanding its metallic appearance, the LIGHTEST FLUID BODY KNOWN.

251. If a little potasium be dropped into a jar of oxy-muriatic gas, it BURNS SPONTANEOUSLY, and emits a

bright red light. In this experiment a white SALT IS FORMED, being A TRUE MURIATE OF POTASH.

252. If a globule of potasium be thrown upon water, it decomposes it with great violence: an instantaneous EXPLOSION IS PRODUCED with brilliant flame, and a SOLU. TION of PURE POTASH IS THE RESULT.

253. If a similar globule be placed upon ice, it will spontaneously BURN with a bright flame, AND PERFORATE A DEEP HOLE IN THE ICE, which will contain a solution of potash.

254. Take a piece of moistened turmeric paper, and drop a globule of potasium upon it. At the moment that it comes into contact with the water, IT BURNS and MOVES rapidly UPON THE PAPER, as if IN SEARCH OF MOISTURE, leaving behind it a deep reddish brown trace.

255. When a globule of sodium is thrown into hot water, the decomposition of the water is so violent that small particles of the metal are thrown out of the water, and actually BURN WITH SCINTILLATIONS and FLAME, IN PASSING THROUGH THE ATMOSPHERE. ·

256. In two or three wine-glasses, each containing some distilled water, diffuse a little newly prepared white prussiate of iron, and exclude the action of the air; by covering the contents of each with a thin layer of oil. If these colourless liquids be now exposed to different degrees of cold, it will be perceived that whenever the water in either of them freezes, the WHITE PRECIPITATE will become BLUE.

To read or practise the foregoing experiments merely for the sake of amusement, may occasionally have its advantages; but a resolution to repeat them, and examine all the phænomena, for the sole purpose of receiving instruction, is what the author would principally inculcate. Let it never be for gotten, that no effect, however extraordinary, or even trivial,

it may appear to us, can ever happen but in consequence of some previously established law of unerring nature. The fol lowing apostrophe of Dr. Darwin to the Fountain of all Good. ness may possibly tend to impress this important truth upon the student's mind :

"Thus, at thy potent nod, effect and cause
Walk hand in hand, accordant to thy laws;
Rise at Volition's call, in groups combin'd,
Amuse, delight, instruct, and serve mankind."

A VOCABULARY

OF

CHEMICAL TERMS.

A.

ACETATES. Salts formed by the combination of any base with the acetic acid. See page 229.

ACIDS. For the nature of acids, see page 170,

oxygenized. Acids combined with an additional quetity of oxygen, for particular purposes. The oxymuriatic acid used in bleaching is an instance of this superoxygenizement. See page 182.

hyperoxygenized. Acids which are oxygenized to a maximum. See page 220.

ACIDULES. A term applied to the natural combination of some acids with a portion of potash. The oxalic acid and the tartaric are the only acids that have hitherto been found in this state of semi-saturation. See page 215. AERIFORM fluids. Fluid substances combined with an additional portion of caloric sufficient to give them the gaseous form. See Gas.

AFFINITY, chemical. A term used to express that peculiar propensity which different species of matter have to unite with each other, or with portions of matter of their own species. See chap. 13.

- of aggregation. A force by which two bodies of the same kind tend to combine, and by which an aggregate is formed without the chemical properties of the substances being at all changed. See page 394.

of composition. A force by which substances of different kinds unite, and by which matter is formed whose properties are different from those of the bodies before their combination. This attraction is stronger in proportion as the nature of the bodies is different, between which it is exerted. See page 395.