On the SWEETENING PROPERTIES of FIXED AIR.

THE very curious fact, that fixed air not only preserves bodies from becoming septic, but is also possessed of the power of restoring sweetness to them when actually putrid, seemed to be established by a number of very accurate experiments adduced in support of the doctrine by its ingenious author. This has, however, lately been controverted by a learned writer, who has favoured the public with an Experimental Inquiry concerning the causes which have been generally said to produce putrid diseases, in which he has recounted several experiments, in direct contradiction to those of Dr. Macbride. The authorities of both these gentlemen deserve considerable attention, and it might seem presumption in me to attempt to decide between them, had I only my own opinion to adduce; but as the accuracy of the following trials was witnessed by a Physician, well known for his medical and philosophical writings, I feel the less diffidence in submitting them to the public. They were made with a view, only, to my own information, having in one of the former chapters recommended Magnesia to be taken in the act of effervescence with an acid, as a corrector and evacuant of putrid bile; but as the event appeared to be so satisfactory, and as a determination of this point is the more important, from the late introduction of fixed air as an article of the materia medica, I hope I shall not be deemed to have impertinently obtruded into the dispute by relating them, and endeavouring to point out what, probably, has been the cause of Dr. Alexander's drawing conclusions, so contrary to those of the other celebrated experimentalist.

In the experiments which Dr. Alexander has related in support of his opinion, he has made use of the following methods. He included pieces of putrid mutton in bladders, one containing four ounces in measure of fixed air from fermenting wort; another the same quantity from wort with a piece of putrid mutton in it; and the third, only about half the quantity from a mixture of bread, water, and saliva. In another experiment, he exposed a slice of beef that had just begun to have the putrid smell, to a stream of air brought over from an effervescing mixture of distilled vinegar and salt of wormwood. In a third, the putrid flesh was suspended in the neck of a wide mouthed bottle, while four ounces of distilled vinegar were made into spirit. minderer. In a fourth, four ounces of air from bottled small beer were confined twenty-four hours with the putrid substance, which in a fifth experiment was put into the neck of a bottle of small beer, while it fermented before the fire for half an hour. In a sixth, the septic body was included in a bottle with eight ounces of air from an effervescing mixture of common vinegar and salt of hartshorn. In one only, out of all these experiments, he found the beef in any-wise sweetened, and even in that single instance, though he at first thought the piece a little changed, yet when washed it recovered its putrid smell. However he confesses, that by bringing over fixed air from several other fermenting and effervescing mixtures, on pieces of meat just beginning to putrefy, they were rendered a little sweeter, though never to such a degree, as entirely to lose their putrid taint.

So very different an account of so interesting a subject was truly mortifying: The old adage, experientia fallax, judicium difficile, seemed to be too applicable to the present occasion. Some cases, in which fixed air used medicinally as an antiseptic, appeared to have produced good effects, had occurred to some of my medical friends[v], and I even flattered myself that I had directed it to good purpose in an instance or two. But if the theory on which this practice was founded should be false, the whole superstructure seemed likely to be destroyed. On revising Dr. Alexander's book, I imagined that I had discovered some thing in the conducting of his experiments, which might account for their terminating so differently from those of Dr. Macbride.

The largest quantity of fixed air which Dr. Alexander made use of in any of these experiments was eight ounces in measure, and in one instance, only two ounces were employed to sweeten the putrid substance. In that where the meat was suspended in a wide mouthed bottle while the vinegar was made into spirit. minderer. no method seems to have been taken to retard the too rapid flight of the fixed air, which, from the quick distribution of the salt, would be soon dissipated. From hence I suspected, that a larger atmosphere, or a longer continued stream of fixed air might be requisite to restore septic bodies to perfect sweetness; and in order to decide this point, the following experiments were instituted, having previously obtained some slices of beef so exceedingly putrefied as to render the foetor of them scarcely tolerable.

EXPERIMENT XXIX.

A bottle capable of containing three pints was filled with water, and inverted into a bason of the same; a tube which communicated with another bottle, in which was an effervescing mixture of chalk and oil of vitriol, was then introduced into the mouth of the former, and a stream of fixed air continued, till the whole of the water was driven out by it. A piece of the above-mentioned putrid beef, fastened by a string to a cork, was conveyed into the bottle, which was corked before it was taken out of the water. The beef, after having been suspended in this atmosphere of fixed air for thirteen hours, was very considerably, though not entirely sweetened. But the air in the bottle seemed to have acquired all the putrid smell of which the flesh had been deprived. Another slice of the same beef was not at all sweetened by exposure, during the same time, to the open air.

EXPERIMENT XXX.

A piece of this beef suspended all night in the neck of a bottle of artificial Pyrmont water[w], was rendered less putrid, though not near so much altered as that in the foregoing experiment. The water was strongly impregnated with the putrid effluvia.

EXPERIMENT XXXI.

Two drachms of Magnesia Alba diluted with two ounces of water were placed in a quart bottle, to which was added a sufficient quantity of the strong spirit of vitriol to let loose all the fixed air from the Magnesia, during the separation of which, another equally putrid piece of beef was suspended in the bottle, which was so corked as to retard, though not totally prevent the escape of the air. Another piece of the same beef, was exposed in like manner to the vapour arising from the addition of oil of vitriol to two drachms of chalk diluted with water. They were suffered to remain for twenty two minutes, and being then examined were absolutely free from any putrid foetor, and though well washed in water continued quite sweet.

EXPERIMENT XXXII.

Air expelled from Magnesia by the nitrous acid, sweetened a piece of the same putrid flesh suspended in the neck of the bottle during the effervescence. The beef smelled of the nitrous acid, but remained equally sweet when washed from it in water. Very little change was produced in another piece exposed to the smoaking spirit of nitre.

It may be some additional evidence in support of the sweetening properties of fixed air, to declare that the highly offensive, sanious discharge of a cancer has been rendered considerably sweeter by it[x]; and that I have seen a case of a dysenteric fever, attended with extremely foetid and bloody stools, in which fixed air was directed, by the Physician who attended, to be thrown into the intestinal tube by way of clyster; the consequences of which were the correction of the putrid smell of the discharges, and the reduction of the inflation of the abdomen, together with contributing considerably to the ease of the patient after each injection of air[y]. A third case of this kind has very lately occurred to Dr. Percival, in which the injection of fixed air removed the foetor of the stools, and the patient recovered without the assistance of any other medicine, except the moderate use of wine as a cordial, and of a decoction of Peruvian bark during the convalescent state. I have also experienced the removal of a very large and deep slough, and the healing of the ulcer in the putrid sore throat, more expeditiously by the inspiration of fixed air than by any other method.[z]

One circumstance in the twenty ninth experiment peculiarly attracted my attention, viz. that the air in the bottle was so very putrid, though the beef exposed to it was restored to sweetness. The septic effluvium therefore did not appear to be destroyed, but to have changed place. From this fact it occurred to me that there might possibly be an affinity between the fixed air and the septic particles, and that this air might act as a menstruum on the effluvia emitted by putrid bodies. I have since had the pleasure to see that Dr. Priestley, whose investigation into the nature of factitious air has lately been laid before the Royal Society, and must contribute to exalt him to a still higher rank as a Philosopher, has taken notice of something similar hereto. I am sensible that difficulties attend this theory. Doctor Percival, in the second volume of his Essays, which is now in the press, has offered some ingenious conjectures on the subject, and to them I refer the reader. I shall only mention one experiment which seems to give some force to this doctrine.

EXPERIMENT XXXIII.

Slips of linen cloth dipped in very rancid oil, had their rancidity much diminished by exposure to a stream of fixed air from an effervescent mixture of chalk and spirit of vitriol. But a pint bottle of the same oil being saturated with this vapour, was equally offensive as before the air was thrown into it, though the oil appeared to absorb a considerable quantity of air.

Dr. Macbride exposed a piece of rag dipped in lixivium tartari, and another tinged blue by the scrapings of raddishes, to the vapour arising from a large vat of melasses wash in high fermentation, without any change being effected in either, which could be supposed to proceed from an acid vapour. But as water impregnated with fixed air has evidently an acidulous taste, and it seemed probable that some of the vitriolic acid might be volatilized during the effervescence which proceeds from its admixture with the alkaline body, when the air is procured from these substances, it was apprehended that the antiseptic and sweetening powers of air thus obtained, might depend on the acid contained in it. In order to evince how far this conjecture was just, Doctor Percival was so obliging to assist me in suggesting and making the following experiments.

EXPERIMENT XXXIV.

Twenty drops of syrup of violets mixed with a glass-full of water were changed into a lively red by the addition of one drop of dilute spirit of vitriol. The season of the year did not allow us to use the fresh juices of vegetables, but this trial shews the genuineness of the syrup of violets, and that it was a sufficiently delicate test of acidity.

EXPERIMENT XXXV.

A paper besmeared with this syrup, was placed over a vessel which contained an effervescing mixture of chalk and oil of vitriol. No change of colour took place except in one small point[aa], which had probably been accidentally touched by the vitriolic acid.

EXPERIMENT XXXVI.

Twenty drops of the syrup of violets were added to a glass-full of water strongly impregnated with fixed air, after the method directed by Dr. Priestley[ab], but without any variation in the colour of the violets.

EXPERIMENT XXXVII.

A few drachms of the syrup of violets were dissolved in half a pint of water, which was afterwards impregnated with air from an effervescing mixture of chalk and the smoaking spirit of nitre; but the syrup of violets suffered no change of colour.

EXPERIMENT XXXVIII.

A piece of putrid flesh which had been sweetened by the vapours of iron filings and the nitrous acid, had a pungent, acidulous smell. It was carefully washed in water, and still remained free from putridity. A few drops of lixivium tartari were instilled into this water without producing any sensible effervescence.

May we not infer from these experiments, that if fixed air be an acid, it is an extremely weak one, and not sufficient, as such, to sweeten putrid bodies; which effect must consequently be owing to some other mode of action, the principles of which are not as as yet positively defined?