gentle heat; alkali is immediately formed by oxygen from the oxyds, which dissolves the glass, and a new surface is soon exposed to the agent. At a red heat even the purest glass is altered by the basis of potash : the oxygen in the alkali of the glass seems to be divided between the two bases, the basis of potash and the alkaline basis in the glass and oxyds, in the first degree of oxygenation, are the result. When the basis of potash is heated in tubes made of plate glass, filled with vapour of naphtha, it first acts upon the small quantity of oxyds of cobalt and manganese in the interior surface of the glass, and a portion of alkali is formed. As the heat approaches to redness it begins to rise in vapour, and condense in the colder parts of the tube; but at the point, where the heat is strongest, a part of the vapour seems to penetrate the glass, rendering it a deep red-brown colour; and by repeatedly distilling and heating the substance in a close tube of this kind, it finally loses its metallic form, and a thick brown crust, which slowly decomposes water, and which combines with oxygen when exposed to air, forming alkali, lines the interior of the tube, and in many parts is found penetrating through its substance.

The basis of soda, is solid at common temperatures. It is white opaque, and when examined under a film of naphtha has the lustre and general appearance of silver. It is exceedingly malleable. Its specific gravity is less than that of water about 9 to 10, or. 9348 to 1.

The basis of soda has a much higher point of fusion than the basis of potash, its chemical phenomena are analogous to those produced by the basis of potash.

The proportions of the peculiar basis, and oxygen in potash and soda are, about six parts basis and one of oxygen in potash, and seven parts of basis and two of @xygen in soda.

PNEUMATIC CISTERN of YALE COLLEGE. AN instrument has been for several years used in the laboratory of Yale College, for experiments in the large way, on the gases which water does not rapidly adsorb,

which has been found to be more convenient and complete than any other arrangement of apparatus for similar purposes. The only instrument of the kind which has ever been constructed, was manufactured in New-Haven. [See Frontispiece.] Being calculated for an extensive course of public lectures, delivered in a laboratory where there is plenty of room, its dimen-. sions are larger than might be worth while in establishments on a smaller scale. Its form is that of a parallelopipedon, 7 feet long, 3 feet wide, and 2 feet 2 inches deep, without allowing for the two inch pine plank of which this part of the instrument is constructed.

The several planks and parts are connected by grooves and tongues, and bound together by iron rods, passing laterally through them, and terminating in screws furnish, ed with nuts. The interior part is furnished with two shelves,, [A.A.A.A.] each two feet six inches long, for sustaining air-jars and bell-glasses; the middle space between these is one foot eight inches wide, and forms a well [H] for immersing the bell-glasses; across this well is placed a sliding shelf, [G] with three inverted shallow tin funnels beneath it, corresponding with as many holes for receiving and transferring gases. Thus far, it is obvious that the instrument is only a very extensive pneumatic cistern, and has no superiority over those commonly in use, except from its affording ample space for a very important and interesting class of experiments, which are much more impressive and convincing to a large audience, when performed on a large scale. There are, however, a number of additional contrivances. Beneath each of the shelves are two inverted rectangular boxes, [shewn by dotted lines at I. I. and under A.A.A.A.] made of thin pine plank, dovetailed together at the angles, entirely open below, and attached to the inferior side of the shelves by tongues, grooves, and wood-screws. These boxes are twelve inches deep, of the capacity of about 12 gallons each, and occupy the whole space beneath the shelves except. 7,5 inches at each end of the cistern, and nine inches between the bottom of the boxes and the bottom of the cistern. This latter space is reserved to give room for the action of three pair of hydrostatic bellows. [B.B.] They are made of leather, nailed to the bottom of the cistern,

4

distended by circular iron rings, and attached by nails. to a thick circular plank which serves as a top, and which is moved up and down by an iron rod connected with an iron lever, [C.C.C.] which rests on a forked iron support, attached to the upper edge of the end of the cistern. The bellows are so placed, that nearly one half projects beneath the boxes, which we may call reservoirs; the other part is beneath the open space which lies between the end of the reservoirs and the end of the cistern, and the rod of the bellows perforates the shelf immediately at the termination of the box and contiguous to it, but does not pass through the box, which must be air-tight. At the edge of that part of the bellows which projects beneath the reservoir, is a valve opening upward; in the centre of the bellows and on the bottom of the cistern, which is also the bottom of the bellows, is another valve opening upwards, covering an orifice which is connected with a duct, leading out, laterally, through the plank, edgewise, to the atmosphere. Into this duct is inserted a copper tube, [D.D.] consisting of two parts, one of which forms merely a portion of the duct, being driven into it so that it forms. a perfectly tight connection; the other part is soldered to this at right angles, and ascends in close contact with the outside of the cistern, till it rises two inches higherthan its upper edge, and there it opens in an orifice somewhat dilated. Each of the four reservoirs may be considered as furnished with the apparatus of bellows, duct, valves, and tube; although in the instrument to which this description refers, there are in fact but three bellows, &c. one reservoir being destitute of them. It remains to be remarked, that each reservoir is furnished with a stop-cock, which lies horizontally upon the shelf and partly imbedded in it, and passes into the reservoir by a short tube of copper, soldered at right angles with the cock.. The cocks of the two contiguous reservoirs are placed parallel to each other and to the sides of the cistern, and immediately contiguous to the partition which separates the reservoirs, and they are connected by a third stop-cock soldered to each of them,. opening into both by proper orifices, and thus serving, when occasion requires, to connect the reservoirs, and in fact, to convert two into one. Through each of the

shelves, at the angles of the two reservoirs which are. contiguous at once to that side of the cistern which may be regarded as its back part, and to the well, a hole is bored into the reservoir for the insertion of a copper tube [E.E for a blow-pipe. These tubes are so formed, that while one part is pressed firmly into the hole so as to be air-tight, another part, at right angles with the first, and bending in a pretty large curve, terminates in a trumpet-like orifice, adapted to the insertion of a cork. Immediately beneath these two orifices is a table, [F.] attached by hinges to the side of the cistern, to sustain a lamp for the blow-pipe; when not in use, it hangs by the side of the cistern, and is raised occasionally, as it is wanted.

To an intelligent chemist, it will be obvious from an attentive perusal of the description, that this instrument will afford all the following advantages.

1. It is an extensive pneumatic cistern, with every common convenience, on a large scale.

2. By the bellows and their appendages, common air may be thrown into the reservoirs, by which means the height of the water on the shelves may be increased at pleasure, when it is too low.

3. By permitting a portion of this air to escape, by opening one of the horizontal cocks, the height of the water on the shelves may be diminished at pleasure; thus we have means of graduating the height of the water precisely to our purpose without lading it out or in.

4. We have four capacious air-holders in the very place where the gases are produced, viz. in the pneumatic cistern; thus, four different kinds of gases may be stored away under water in a space otherwise useless. For instance, common air, for regulating the height of the water, or, for the blow-pipe, may be in one reservoir; oxygen gas in a second, hydrogen gas in a third, and olefiant gas in a fourth, and they may be thus reserved for future use.

5. The gases may be drawn off for use into bellglasses, merely by bringing those bell-glasses, filled with water, over the horizontal cocks.

6. It is obvious that the four reservoirs are in fact four large gasometers; they want nothing to entitle them to this character, except a scale which a moderate share of ingenuity would easily adapt, to them; the gases may be delivered into them at once by crooked tubes passing from the gas-bottles, and any gas contained in a bell-glass may be thrown into a reservoir, by a single stroke of the bellows. For this purpose a crooked tube connected with that which leads to the bellows and terminating in the well beneath an air jar, is all that is necessary. Or, by baring the arm, the gas may be thrown up by the hand, into the reservoirs, the jar being pushed down through the water,

7. It affords an excellent blow-pipe for common purposes and for the fine experiments with oxygen gas; and, by fitting to it Mr. Hare's very ingenious apparatus of the silver cylinder, it becomes the compound blow-pipe, for the invention and appli cation of which he deserves so much credit. By the same contrivance water is formed with the greatest facility by burning the two gases as they come from their respective reservoirs, and issue at a common orifice, covering the flame with a receiver.

8. The inflammable gases being confined beneath the pressure of water, will issue at any orifices, where they are permitted, and thus all the ornamental as well as useful purposes to which the combustion of these gases is applied, may be exhibited; particularly, the gas from fossil coal may be made to burn in revolving jets, stars, and other fanciful and useful forms, merely by substituting for a blow-pipe tube, the apparatus proper for this exhibition.

All these purposes, this instrument has fully answered during several years; and it may be confidently recommended to lecturers on chemistry, and, on a smaller scale would be very valuable to a private chemist, A forcing pump might be substituted for the bellows, with a saving of the space which the bellows occupy, but it would be probably less convenient in practice.

This first idea of this instrument was suggested by Mr. Hares compound blow-pipe. Being mentioned to that gentleman, the subject was prosecuted in common, and so far matured that it was afterwards executed by the writer, B. SILLIMAN.