plant, of any sort whatever, is put into a jug full of water, and left there during the darkness of the night, whether in the open air or in the house, it will be found that it has given a little air, but of such a nature as to be totally unfit for respiration, and in general of so poisonous a quality as to extinguish a flame in an instant, and to kill an animal in a few seconds; the same consequence would result from this experiment if the jug was put in a dark place during the day time. Notwithstanding that plants exhale but so very small a quantity of cor

rupted air in the dark, they are nevertheless capable of shedding a terrible poison into a considerable mass of common air, in which they are confined, and of rendering it ab solutely mortal to the animal who breathes it; a handful of leaves can, in one night, poison two pints of air, so as to kill an animal in less than a minute. But if plants, being in the shade, or in the dark, produce so dangerous an air, the same plants, exposed to the rays of the sun, diffuse the purest of all air.

"If we examine the air that forms those bubbles (the plants exposed to the sun under a vessel of glass filled with water), we shall soon be convinced that it is far from being common air, we shall find it of a very superior quality to the best air of the atmosphere, it being truly dephlogistical; an animal would live a longer time in it than in the purest common air; it augments considerably the volume of the flame of a wax candle, and gives it a brightness which dazzles the eyes; it will rekindle the flame of a wax taper, if the least particle of fire remains on the wick.

"But what is very strange in this great phenomenon is, that the pro

duction of this perfect air cannot be attributed to the heat of the sun, but to its light only. the following experiments leave us not any doubt on the subject.

"If the production of this air was caused by the heat, instead of the light of the sun, there would not be any reason why the plants should not give the same air when placed in the shade, during a very hot day, or brought so near to a fire as to receive the same degree of heat as that acquired in the sun, but the contrary of this happens. I put a certain number of leaves into a vessel filled with water, and turned it down; I exposed it to the heat of the fire, so as to heat it to a degreenearly equal to that of another vessel of the same size, filled in like manner with the same quantity of leaves from the same tree, which I had placed in the sun: the result from these two experiments was, that the air I obtained from the leaves placed by the fire was mephitic, and that obtaiued from those leaves exposed to the sun was dephlogisticated air.

"I placed an equal quantity of walnut leaves in two vessels of the same dimensions, one I put on the top of a wall in a brilliant sun, and the other under some rasberry bushes, that were so tufted as to be inpenetrable to the rays ofthe sun: this last mentioned vessel was left there the whole day, and had acquired a degree of heat equal to that of the atmosphere. (the thermometer of Fahrenheit being then in the shade, in the middle of the day, at seventy-six degrees.) The vessel exposed to the sun was not left long enough on the wall to have acquired a degree of heat equal to that of the atmosphere. Those leaves placed in the shade

had

had given a very little air, which was of an inferior quality to the common air; whilst those leaves exposed to the sun, and had received very little heat, had produced a considerable quantity of dephlogisticated air.

"Plants do not give dephlogisticated air in a room, however warm it may be made, if the sun does not shine on the vessel in which the leaves are contained.

"If plants possess an obnoxious quality in the shade, nature has happily endowed them with the faculty of repairing in the sun the mischief they may have occasioned." It is not the same case with flowers; they captivate the eye and the smell, but they are, at the same time, very prejudicial in a place where the air does not circulate; they exhale, at all times, whether in the night, in the shade, and even in the sun, a deadly air.

Dr. Priestly had observed, "That a rose shut up between two glasses, had corrupted the air in which it was inclosed to such a degree, as to render it unfit for breathing;" and from thence he concludes, with reason, that the air of a room may be infected by such flowers.

"Ihave tried an experiment upon all the flowers I could find in my neighbourhood, and have not met with one that did not at all times spoil the air, more particularly when the stalks were put in water. Flowers under water exhale a little air; but very slowly, and in a very small quantity, but the air is of the most poisonous quality. When they are in the common air, they corrupt it in a few hours, and render it entirely unwholesome. Their pernicious influence is so inherent, that it is not in the power of the sun to dispel it. A nosegay, composed

of about thirty honeysuckle flowers, the agreeable perfume of which is so generally known, spoiled, in three hours time, two pints of air, in the middle of the day, to such a degree. as to prevent the burning of a candle. These flowers, after hav ing corrupted a large mass of air, did not in the least lose their sweet scent, with which they impregnated the poisonous air. So that persons who indulge their taste for those flowers, may very easily place them. selves in the most imminent danger of perishing.

All fruits in general exhale a dan. gerous air, whether by day or night, in the sun or in the shade, and communicate a most unwholesome quality to the surrounding air.

"I was astonished, and even a little sorry," continues M. IngenHousz, " to discover a hidden poison in the fruits, which constitute so great a part of our food, and the more so, as I found in some of those, the most delicious to the taste and smell, this poisonous quality pre+ vailing in the most surprising de gree; such as in the peach. It appears to me that the unwholesome qualities of some fruits, surpasses even that of flowers.

"I have observed, that a peach in the shade can so corrupt a mass of air, six times greater than its own size, as to render it absolutely fatal to an animal that should breathe it; and that this same peach may render the like quantity of air so corrupted, even in the midst of the sun, as to extinguish immediately a wax candle."

Here follows an experiment very applicable to the subject we are treating upon.

"A jug made of a size to contain eight pints, filled a third part with mulberries quite ripe, and turned

downwards

downwards on a plate, was placed in the sun for the space offour hours at the end of which time the air in it was so corrupted as to extinguish a candle immediately."

Enough has been said on the subject to convince us, that since leaves exposed to the shade produce a mephitic gas, it must be of the highest importance not to keep the mulberry leaves destined for the feed of the silk-worms in the same room with them: it is absolutely necessary then to have some separate airy room to serve for the purpose of a store-house for the leaves; it is also essential to let them remain at least four hours before they are carried into the store-room, to give them time to cool, and to shed their first effluvium, which is always the strongest and the most abundant. I would likewise advise to have the leaves stirred about before they are given to the silk-worms, and the perni dious air dispelled by the waving of napkins strongly too and fro about the room, with the windows and doors set open,

Experience alone had already taught that the leaves should not be given the moment they were ga. thered; and careful people have always attended to the making of a provision of them beforehand; and when this custom has been deviated from, the most fatal and sudden accidents have ensued to the silkworins, they have been so affected by the mephitic vapour as to perish in a very short space of time; those who are accustomed to raising of silk-worms called this accident, une mauvaise donnée. But without knowing from whence proceeds the cause, they are sensible that it might have been avoided, by letting the leaves remain some time after they were

gathered before they were used, and they feel themselves culpable offorgetfulness or want of attention upon the occasion; the excuse then pleaded is, that the badness of the weather having obliged them, for want of leaves, to keep their silkworms fasting, made them in such haste to give the improper food; it would, nevertheless, have been much better to have kept them some hours longer in want of sustenance. In spite of every precaution that can be taken, it is not possible to banish totally the effluvium of the leaves when their meals are distributed, because, not only from the large quantity of leaves requisite, more especially when the silkworms are in an advanced state, but likewise from these insects tearing of the leaves, which accelerates, in a greater degree, the mephitic effluvium; this proves still more forcibly how necessary it is to admit the fresh air, from whence I am led to believe that it would be best to establish a free current of air in the spinning place, by the making of two windows, opening them at the feeding time, and leaving them so for at least half an hour, during the height of the repast, if the weather will admit of it.

It has been proved, from what has been said on the subject of flowers, how pernicious their influence is; they should therefore be entirely banished from wherever silk-worms are kept; notwithstanding which, the contrary method has been practised down to the present time, above all by the peasants, who take much pleasure in adorning their spinning places with flowers; and heaven knows what choice they display; the preference with them is always given to the largest

sort

sort of flower, and to those that are most strongly scented; they form large nosegays of honey-suckles, of lillies, of elder-flowers, &c. These good people, however, act on a prin çiple drawn from their own method ofliving, and only err because they cannot suppose that flowers can shed a malignant vapour, so foreign to their sweet scent; their houses are not, in general, either too clean or agreeably perfumed. The exhalations from the dunghills of their farm-yards, the preparations oftheir kitchens, where garlick, onion, cheese, and the smell of frying always reigns, form fœtid vapours, which scarcely ever quit their habitations. Having learnt, from experience, that the silk-worms love cleanliness and a pure air, they take some care about it, and mean, by the perfume of the flowers, to correct the above-mentioned bad smells.

Fumigations are likewise much in Vogue with these people, and each varies them according to their taste and fancy; the following are those in which they place most confidence, and to which the preference is given by them, gunpowder, incense, rosin, juniperberry, lavender, vinegar, apple-parings, sugar, ham, and lard: all these fumigations, lavished without any order or method, serve only to spoil or to load the air, and should be banished, to the reserve of one only, on which we shall treat hereafter.

Fruits being at least of as pernicious a quality as flowers, should be equally kept at a distance from the place where the silk-worms are; the trunks and chests of drawers of the peasants are never unprovided with such articles; apples above all others, the smell of which is in general so disgustful, is to them a

grateful perfume, and used as such by the women for scenting their linen, and yet the effluvium of this sort of fruit is fatal.

There should not then absolutely besuffered to remain either fruits or flowers in the spinning place. But as we have seen by the experiment made on mulberries, by Dr. IngenHousz, that this fruit produces a poisonous air, the greatest care ought to be taken, more particularly. when ripe, to pluck them off and separate them from the leaves; it is in vain to object against it, by alleging that the silk-worms love and eat them; for do we not eat peaches without being incommoded by them, notwithstanding the malignity of their effluvium when shut up in a close place. Is not the mephitic gas a poison when breathed, and a remedy when mixed with water?

It is, therefore, to be wished that all the mulberries, not only those that are ripe, but those likewise that are young and green, an abundance of which insinuate themselves amongst the leaves, should be carefully taken away; their insipid, and at the same time strong, smell announces abundant exhalations; and their watery particles accelerate the fermentation of the litter. I feel the difficulty that must attend the separating of them when small, when the demand for the quantity of leaves is considerable; but the pains must in that case beredoubled, and none must be left to remain that approaches to being ripe.

Before the modern discoveries made on the different sorts of gas, it was not doubted but that in these hidden springs consisted the principles of sickness or of health; and although we have here given but a rapid sketch of this, relatively to

the

the silk-worms, those persons who are not versed in these matters have nevertheless seen enough to be convinced that the different kinds of gas may happily, in many cases, be rendered profitable. There is even room to hope, since so many estimable learned men employ them selves in researches on the nature and quality of air, that new discoveries will not fail to succeed those already made.*

On the influence of oxygène on colours; from Nicholson's Translation of Chaptal's Chymistry.

COL

NOLOURS are all formed in the solar light. The property which bodies possess of absorbing some rays, and reflecting others, forms the various tinges of colours with which they are decorated, as is proved from the experiments of Newton. But in what manner do the coloured bodies of the three kingdoms of nature accqire theproperty of constantly reflecting one determined kind of rays? This is a very delicate question; for the elucidation of which I shall bring to gether a few facts.

It appears that the three colours which are the most eminently primitive, the only colours to which we need pay attention, that is to say, the blue, the yellow, and the red, are developed in the bodies of the three kingdoms, by a greater or less absorption of oxygène, which combines with the various principles of those bodies.

In the mineral kingdom, the first impression of fire, or the first degree of calcination, developes a blue colour, sometimes interspersed with yellow, as is observable when lead, tin, copper, iron, or other metals, are exposed in a state of fusion to the action of the air, to hasten their cooling. This may be especially observed in steel plates which are coloured blue by heating.

Metals acquire the property of reflecting the yellow colour by combining with a greater quantity of oxygène; and accordingly we perceive this colour in most of them, in proportion as the calcination advances. Massicot, litharge, ochre, orpiment, and yellow precipitate, are instances of this.

A stronger combination of oxygène appears to produce the red; whence we obtain minium, coleothar red precipitate, &c.

This process is not uniform through all the bodies of the mine-* ral kingdom; for it is natural to infer that the effects must be modifi ed by the nature of the base with which the oxygène combines. Thus it is that in some of them we perceive the blue colour almost immediately followed by a black; which may easily be accounted for, on the consideration that there is a very slight difference between the property of reflecting the weakest rays, and that of reflecting none at all.

To give additional force to the observations here made, we may also take notice, that the metals themselves are most of them colourless, and become coloured by calcination;