DESCRIPTION OF JOHNSON

TOFTS'S BLOW-PIPE.
(From a Correspondent.)

A GLASS-BLOWER invented an instrument, or chest, into which enough air might be at once blown from the mouth to urge the flame of a common lamp for near five minutes; but the shortness of time during which it continued to propel the air, and the interruption occasioned by having to supply it every five minutes with fresh air, induced Dr. Clarke to lay aside the use of it.

A servant of his, one Johnson Tofts, who often attended at these lectures, took the liberty of asking why his master rejected it; and the cause being explained to him, he, without any help from his master, examined it, and then fell to work and produced an apparatus, which possesses many great advantages over the old construction. This new instrument was two feet high, two feet long, and five inches broad. The cavity was divided into two chambers; the upper one, Q, about thirteen inches deep, and the lower, PP, about eleven. A pipe, O, open at both ends, and two inches in diameter, opens at top into Q, and reaches to within half an inch of the bottom of PP, forming a communication between the two chambers. Two pipes, F and E, arise from the chamber PP, and come out at the top of the chest, each furnished with a stop-cock. The pipe, F, serves to replenish the chamber,

PP, with either common air, or any gas, from a bladder or syringe. The pipe E has its orifice bent down to receive jet pipes, for the purpose of propelling the flame of the candle or lamp X; a small opening, H, is left in the top, opposite the pipes F and E.

When this is to be used, some water is first introduced by the pipe F, or the opening H, so as to fill the chamber PP, the pipe O, and cover the bottom of the chamber Q. Common air, or any gás, is next forced through F, into the chamber PP, which forces the water in PP up the pipe O, into the chamber Q, the air in which escapes by the opening H. If the stop-cock of the pipe E be now opened, a jet of air is propelled on the flame by means of the pressure of the water in Q.

The advantages of this instrument are, that the operator has his hands at liberty, and is relieved from the trouble of blowing; and also it possesses advantages which the old instrument did not, viz.—it allows the use of any gas unmixed with common air; it may be kept any time without using it, and may be prepared for use in a moment, by merely lighting the candle or lamp. It is very powerful.

INCANDESCENT TEMPERATURE OF PLATINA WIRE. M. ERMAN has ascertained the temperature which a platina wire of certain dimensions must have to be incandescent when it is immersed in a current of hydrogen gas. A hollow place in a small mass of iron was filled with mercury, in which was plunged a thermometer and a very fine platina spiral wire; near it was the mouth of a gasometer, supplying at pleasure a current of hydrogen gas. A lamp placed under the iron heated the wire gradually, while its temperature was indicated by the thermometer. He observed with surprise that 410 7 of Reaumur, or 126o of Fahr. was sufficient to make the platina red hot in the hydrogen gas.-Annales de Chimie et de Physique, T. 25, p. 285.

THE present plate represents a very convenient gasometer for holding oxygen gas. It is made of tinplate, well japanned, both withinside and without. It may be of any size: the vessel, of which this is a representation, held about 2000 cubic inches. It is a cylindrical vessel, close on all sides, and ought to be pretty strong, to resist the pressure of the atmosphere, which tends to force out gas, or to force in air, according to the changes in its density which take place. It is furnished with three mouths, A, B, C. The first at the top, the second at the side as high up as possible, the third at the bottom. A and B are each provided with a stop-cock. The stopcock, at A, belongs to the tube, D, which goes to the very bottom of the vessel into which it is soldered, in order to increase the strength of the air-holder. The tube, D, towards its bottom, is perforated with a number of holes. To the extremity of the stop-cock, B, the piece of bent tube, E, is ground, so as to be air tight, but to move freely round the extremity of B, which is turned up to receive it; and to the extremity of E the long tube, F, is likewise ground, so

as to be air tight, yet capable of moving freely. These two tubes, by their motion, form an universal joint, so as to enable the operator to turn the extremity of the tube, F, any way he thinks proper. The mouth, C, consists of a tube about an inch in diameter, introduced into the vessel near the bottom, at an angle of about 45°. It is provided with a stopper, which screws into it and shuts it close. Gis a glass tube, fixed into the top and bottom of the air-holder, and graduated. The use of it is to show the operator how much gas the vessel contains.

A few words will explain the method of using this vessel. The first step is to fill it with water. For this the mouth, C, must be shut, and the stop-cocks, A and B opened. Water is then poured into the glass vessel, H, which, running down the tube, D, makes its escape through the holes in its bottom, and fills the vessel, while the common air makes its escape by the stop-cock, B. When the air-holder is quite full of water, the stopcocks, A and B, are to be shut, the glass vessel, H, removed, and the stopper of the mouth, C, removed. As the vessel is completely air tight, the water cannot make its escape by the mouth, C,

because the angle at which it enters the vessel prevents any common air from entering. The mouth of the tube connected with the apparatus for furnishing oxygen gas being introduced into C, the gas rises gradually to the top of the air-holder, and the water runs out by the mouth, C. When the process is finished, the mouth, C, is to be shut; and if the vessel be a good one, the gas may be kept in it for many months without undergoing much alteration. Suppose we want a portion of the oxygen gas out of this air-holder, for any particular purpose, we have only to introduce the point of the tube, F, into the mouth of the vessel which we mean to contain the oxygen gas, and then to pour a quantity of water into the glass vessel, H, which must be replaced for the purpose. The stopcocks, A and B, being opened, the water runs down the tube, D, and forces the oxygen gas to escape through the tube, F. By this method any quantity of the gas wanted may be easily procured.

THE CULTIVATION OF
COTTON.

(Continued from p. 160.) THE name of cotton is given generally to a soft downy substance which envelopes the seeds of various plants; but that particular species of this downy substance, which is so extensively employed for making garments, is the produce of a tree or a shrub, of which there are several species known to botanists, under the generic name of gossypium. It belongs to the class monadelphia, order polyandria, and possesses the following cha racters: Calyx double; exteriorly three cleft. Capsule quadrilocular. Seeds involved in cotton. Botanists enumerate ten species of gossypium, namely Herbaceum, Indicum, Micranthum, Arboreum, Vitifolium, Hirsutum, Religiosum, Latifolium, Barbadense, Peruvianum. Only a few of these species are cultivated, and principally the herbaceum, arboreum, and the hirsutum. The mode in which it is cultivated depends on the cir

cumstance of the shrub being annual or perennial. In general, the annuals thrive best in a dry, gravelly soil, and are said to prefer old to new ground. The culture begins in the rainy season, about March or April. Holes are made in the ground in rows, at the distance of from seven to eight feet, and a quantity of cotton seed is put into each hole. In a short time the seeds germinate; and as soon as the young plants rise to a height of six or seven inches, they are all, except two or three of the most vigorous, pulled up by the root. The plants allowed to remain are kept pruned down to the height of about four feet, which enables the husbandmen to gather the cotton easily without diminishing its quantity.

On the coasts of Guiana and the Brazils, the perennial cotton is almost exclusively cultivated. The soil, in the former, is chiefly alluvial mud, being deposited by_the rivers that there empty themselves into the ocean. The country is so low, that inundations are frequent; and to carry on cultivation of any species, it is necessary to intersect the land with ditches. To plant cotton, the soil is prepared by forming beds of 36 feet in width, slightly elevated in the middle, which are surrounded by drains that carry off the water into the ditches. To take means for keeping the land dry, or at least not to allow water to rest in it, is essential, as stagnant water is pe culiarly injurious to the roots of the cotton tree. When the beds are thus prepared, holes are dug about five feet apart in every direction; a little light earth is thrown into every hole, and on that a small handful of cotton seed, and then the earth is raked over the holes. The planting, in general, takes place in showery weather, and in three or four days the young plants rise above the ground. Within a month they attain the height of four or five inches, and all except three or four in each hole are pulled up by the root. The ground is carefully weeded every month, and at the

third weeding, only one plant is left in each hole. When the plants are about eighteen inches high, the tops are cut off to make them put out lateral shoots. The usual period of planting in Guiana is December, January, April, and May; if the planting takes place in the two former months, the tree requires to be pruned in June; if, in the two latter, the plant only requires to be nipped with the fingers, and begins, if the weather be dry, to yield cotton about the month of October. The trees do not however produce a full crop till the second year, and, in general, they last only five years. Wherever a tree fails, its place is supplied; but, there is no regular period of replanting. After the trees are a year old, they are regularly pruned once a year, between April and July. If the season be favourable, the trees begin to blossom about the end of July, or the beginning of August; the pods form in succession; begin to open in about six weeks; and at the end of October, the first picking begins, which is not completed till the end of December. The rainy season then begins, during which the trees vegetate with great vigour, and again blossom. If the weather be fine, a second gathering begins at the end of February, and is completed about the middle of April. In Guiana, however, the second crop frequently fails, owing to a cold northerly wind, which either shakes the blossoms, or the pods fall off; or, if the latter arrive at maturity, the seed and the cotton stick together, and cannot be separated with advantage.

In the West India islands, and in Georgia, the same mode of cultivation is practised; but there, owing to some local peculiarities, the trees are annually renewed. The blue clay soil which is daily forming on the shores of South America, is found to be peculiarly favourable to the growth of cotton; from which circumstance it has been concluded, that salt is a good manure; and accordingly, where it can be done, the land is fre

quently flooded with salt water, and, it is said, with considerable benefit. Even sandy and gravelly soils, which are situated near the sea, and can be thus flooded, are found to be very productive.

The cotton is all gathered by the hand; and, in general, it is no where cultivated but by a slave population. After the harvest is completed, the cotton is dried in the sun, until the seed becomes quite hard, otherwise it would heat, ferment, and spoil. This takes about three days, during which it is exposed on a wooden or a tiled platform to the rays of a tropical sun. The seed is then separated from the cotton, by passing it through between two slightly grooved wooden rollers, of one quarter of an inch in diameter, which are driven by treadles put into motion by the foot, while the cotton is pressed through by the hand. This machine is called a gin, and a good workman can separate from 50lbs. to 60lbs. a day; but the labour is severe, and the slaves are not kept at it more than a fortnight at one time. Several machines for cleaning cotton have lately been adopted, and are coming into general use, as it is found to be a great saving of labour to prepare it, as far as possible, before transporting it. After it has been ginned, it is carefully picked by women, who free it from broken seeds, dried leaves, and yellow or discoloured locks of cotton. An expert woman cleans from 25lbs. to 30lbs. a day. Some people beat it with switches, which facilitates the cleaning; but as this does an injury to the cotton, it is not generally practised. After the cotton has been thus dried, separated, and cleaned, it is packed up in large bags, into which it is pressed by a screw, and in this state is sent to market. The other processes to which cotton is subjected, till it finally assumes the character of cloth, are all carried on with greater skill in Britain than in any other country. They may all be classed under the heads of preparing the cotton for the spinner, spinning, weaving, bleaching,

and dyeing or printing; and on each of these processes we shall, in a future Article, say a few words. The present article will be closed by some observations on the expense of the cultivation of cotton, and the diseases to which the plant is liable. Of course the expense of cultiva tion varies with the situation, and is found to be least in India and America, and greatest in our colonics. In the latter, the capital vested in every acre of land devoted to the cultivation of cotton, including slaves, buildings, &c. amounts on an average to 150l. Each acre on an average yields about 200lbs. of cotton; the expense of cultivation alone amounts to 7d. per lb.; while the expenses of transport, and other mercantile charges, may be about 7d. more. In 1808, the average of the sale prices was 3s.; but in other years the prices have been much lower, and, on some occasions, not sufficient to cover the expenses.

The cotton plant is subject to the ravages of a most destructive species of caterpillar, about an inch in length, and of a most beautiful appearance. A very fragrant smell, which may be perceived at the distance of one hundred yards, issues from the plant on which this caterpillar is feeding, though neither the animals nor the leaves of the plant have of themselves any remarkable peculiarity of odour. Another singular circumstance is, that this insect wholly disappears for a season, and then returns, redoubling its ravages, and extending them with rapidity over every field of the plantation. Though it sometimes destroys the whole crop, no effectual remedy for the evil has yet been adopted. Like other plants, also, it is sometimes injured by blights, which are as destructive as the caterpillar.

We cannot conclude this article without remarking, that there is one thing connected with the cultivation of cotton, which, as the prosperity of our country, and the happiness of so many of our people, now depend on this plant, fills us with regret. It is almost wholly

the produce of slave labour, and the extension given to the cultivation of cotton has increased the number of slaves. This is only an accidental circumstance, however, arising from the barbarous policy which was formerly pursued in colonizing the islands and continent of the new world, and is not necessarily connected with the cultivation of cotton. It serves, certainly, at present to diminish the pleasure we might feel, were the increasing use of cotton, which seems, on a variety of accounts, deserving of preference as the material for clothing, to occasion an increase in the number of free, rather than of slave cultivators; but we do not despair that this may ultimately be the case, and then there will be no alloy to that benefit which, as we noticed in our last Number, has arisen from the discoveries of Hargreaves, Arkwright, and others.

THE GALVANIC PILE. (In answer to a Correspondent.) We do not know whether we shall be able, in the compass of this small Article, to give F. E. all the information he requires, because we are quite in the dark as to what he already knows, and to describe the different kinds of galvanic piles and troughs, the mode of using them, and the principles on which they depend, would take up too much of our space at present; we must, therefore, content ourselves with answering his questions. A galvanic pile is thus constructed:Take a number of picces of the metal called zinc, say 50, they may be of the size of half a crown, if larger the action is more intense; 50 pieces of copper of the same size, and forty-nine pieces of cloth, somewhat less in diameter than the metals, which have been soaked in a saturated solution of common salt, or in water containing the thirtieth part of its weight of sulphuric, nitric, or muriatic acids, and place these three different substances in the following order :First, a piece of zinc; second, a piece of copper; and third, a piece of cloth: fourth, a piece of zinc;