PRE
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cjit falts on the folution in aqua Fortisj and in thefc djfqjiifi- tions it appeared, that thofe falts which gave the mercury a yellow or a red colour, only produced this effeft, as they had been expofed to a longer or a {horter calcination, by which their acids had been driven out, and particles of nre received in their places, and retained there, mfomuch that theie all heat water on being put to diffolvc in it, as they contain a laro-er or fmaller quantity of thefe particles. Now as it is evident that thefc falts give a heat to water, by no other means than by the fiery particles they contain, it is very naturally fuppofed, that they give the yellow or red colour to the dif- folved mercury, by the fame means as we know that thefe are the colours that fire itfejf gives to this body. Thefc falts, before their calcination, make no fuch change in mer- cury: and it appears, that they act upon it as alkalies only, or bodies which have palled a violent calcination ; and that the fiery particles they contain make them aft upon it as fire would ; and upon the whole, that fire and alkalies produce the fame effects on the folution of mercury in aqua fort ia.
On the other hand, thofe falts which have not been expofed to the aftion of fire, and which cool, inftead of heating the water they are diffolved in, or fuch as having been calcined have acquired but little of an alkaline nature by the procefs; that is, have collected few particles of fire in the place of the few acid particles which they have loft; thefe do nothing to the dillblved mercury but carry off a part of its acids, its whitenefs being not at all ;<ffefted by them : nay, even fait of tartar, which is a very powerful alkali, if there be acids mixed with it to drive off the fiery particles it contains, and place themfelves in their room, becomes wholly like one of thefe falts, and makes no change in the colour of the mercury.
In fine, the volatile falts, if they are pure, always give a white precipitate from the folution of mercury; but as thefe falts ufually contain a large portion of oil, this generally be- comes feparated from them in the operation, and mixing it- lelf with the precipitate, makes it of a mixt colour between its own natural white and the natural colour of the oil. As thefe oils in the falts have paffed a ftrong fire, they are ufually burnt, and naturally of a blackifh colour; and therefore the refult of their mixture, with the white precipitate, is a dirty grey. On the other hand, when urine is ufed, as the oily matter attending its falts has not been burned by fire, and as it naturally, by becoming exalted, by fermenting with the folution, acquires a deep blood-red colour, the confequence is, that the precipitate is of the middle colour between this blood-red and its own natural white, and fhews itfclf of a pale damafk rofe colour.
Thefe are the effects of the ahforbent falts, when added fing- ly to the folution of mercury ; the next thing to be enquired into is, how they aft when added one after another to the fitme quantity of the folution? When we have given this fo- lution a yellow colpur, by adding fait of tartar, which, as an alkali, occasions that effeft ; if we afterwards pour upon th-fi fpirit of fal armoniac, or other volatile fait diffolved in plie^m, and raifed by diftillation, the yellowifh or reddifh cobur immediately difappears, and the whole becomes of a dir.y greyifh colour, which afterwards becomes blackifh ; but if cil of tartar, per deliquium, or any other powerful alkali be aided, it does 'not again deftroy this colour, and produce wha: it naturally would, if fnnply mixt with the folution, but only extends the dark or blackifh colour which the mkt matter before had received from the fpirit of fal armO' ni:c.
If fait of tartar, or any other fixed alkali be added to a fo- hiion of mercury, which has before been rendered white by amixture of common fait, or any other fait that has little al- kli in it, the liquor becomes immediately yellow, and that olour remains unalterable by any frefh addition of fait what </er. Salt of tartar is therefore in this cafe to the other falts that the fpirit of fal armoniac is to fait of tartar. If oil of trtar and fpirit of fait be alternately added to a folution of nercury, the folution becomes alternately yellow and white, ccording to the laft liquor that was added ;' fo that thefe two 'ppofite liquors fcem to be of equal force, each making the Diution of the colour it naturally gives, when fuperior to the ■ther in quantity. Thus far, however, only two different iquors have been mentioned ; it is poftible to employ feveral itliers in the fame ' manner one after another, and by that neans to produce many more changes of colour in the folu- ion. All that is to be taken care of in this experiment is, that he weaker liquors be ufed firft, fmce otherwife they cannot iroduce any change ; and what is to be concluded from the v hole is this : i . That mercury when it is penetrated by acid pints, is naturally of a white colour. ?.. That when it is hanged to' a red or yellow colour, it is wholly owing to par- icles of fire introduced into it. 3. *That it never changes
- om white to red, or from red to white again, otherwife
ban by receiving or parting with the fiery panicles it had be- are received. 4. That when the folution acquires a colour, ie mercury lofes its acids, or part of them. 5. That every ime it changes its colour it either lofes it acids, or gains frefh lies i and that this lofing and gaining its acids, is a condition
without which the mercury can neither admit, or throw off the particles of fire. 6. That when an abforbent does no- thing to the folution but take away the acids, without com- municating any thing to the mercury in their place, it always gives a white colour to the precipitate, or to fpeak more pro- perly, it makes the precipitate appear in its proper colour. 7, 1 hat it makes fume other colour appear, when in the place of the acids, of which it has robbed the mercury, it gives it other fubftances which colour it according to their nature and quantity. & That in feveral abforbents calculated to pro- duce feveral colours, that which is the molt powerful alkali is always capable of deftroying all the reft; but that there does not neceflarily follow a change of colour, on the liquor be- coming altered from a lefs alkaline to a more ftrongly alkaline nature. 9. That a liquor of a very ftrongly alkaline na- ture, added to the folution after one which was a weaker al- kali, will make no change in the colour of the liquor, if it have no other efKeft than the abforbing more of the acids from the precipitate, and does not give it other particles in the room of thofe acid ones which it takes away ; and, finally, that weak acids are capable of changing the precipitate from red to white, hut that ftrong ones utterly deftroy all colours. Mem. Acad. Par. 17 14. PREDY, a fea word Signifying the fame as ready. Thus, pre- cly the Jliip, or predy the ordnance, is as much as to make things ready for a fight. Predy the hold, is to lay or flow every thing . there in its due order and proper place. PREGNANCY, graviditas, (Cycl.) the ftate of a woman go- ing with child. This is a time in which women fuffer many diforders, which tho' no way to be cured abfolutely but by- childbirth, yet may be greatly mitigated by medicines. Be- fore any one venture to do any thing, however, in thefe or the like cafes, it is very neceffary to be perfectly affured, whe- ther the patient is with child or not ; and this is known by the following fymptoms, in cafes where there is no occafion for diffimulation, or no other diftemperature joined with this; but when the woman chufes to conceal it, and there is a complication of diforders, the utmoft proofs amount but to prefumptive ones.
The ftoppage of the menftrual difcharges is the firft fign of it, provided that there be no other apparent caufe. But this, tho' the moft plain and obvious fymptom, is by no means a certain one; for a fuppreffion of this kind may happen from latent caufes. A fecond fymptom is, a particular jiaufea at the fight of meat, or even the fmell of itj while the perfon is otherwife well in health, and can eat heartily of other foods; A third fymptom is, a fwelling of the belly; which appears regularly round or globofe, not irregularly protuberant, as is the cafe in diforders of the liver, and other viicera. This fwelling, alfo, increafes placidly, and without the ler^s fwell- ing, or any other fymptom, if the perfon is otherwife in health. After this, the twentieth week of pregnancy gives the moft certain of all the figns, the motion of the fe- tus ; but this is to be carefully diftinguifhed from motions of the bowels in flatulencies, which often fo much refemble it as to deceive the unwary.
If the mother has a mind to hide the fymptoms, the thing may, however, ufually be found out at this period ; for if a cold hand be laid upon the belly when warm, or a warm hand when it is cold, the fcetus ufually foon ftirs, and the very figure and appearance of the belly will give very pro- bable aflurances to a perfon accuftomed to fuch infpeftions. In cafes of a certain conception, a living fcetus is only to be diftinguifhed from a mole or falfe conception by its moving ; therefore when a perfon grows toward the full time, without ever perceiving the child to ftir, it is very much to be fuf- pefted that it is a mole ; which alfo is the more probable, if the menftrual difcharges have come on at times and irregular- ly, during the time, and the fwelling of the belly be irregu- lar, the woman fubjeft to violent flatulencies, and efpecially if fhe go beyond the natural period of nine months'. Thefe fymptoms are not all, however, to be expefted in every pregnant woman; for many of the laborious people of the lower clafs of life, go thro' their whole time in the midft of fatigue and trouble, and that without any of thefe fymptoms ; fo that they are in a great meafure to be attributed to the courfe of life, not the courfe of nature, in the pregnant wo- men of better fortunes. Thofe women are moft fubjeft to them who are of a tender and delicate frame, and thofe who are of a plethoric habit, an idle life, or given to intempe- rance, or fubject to paffions of various kinds, fear, anger, grief, or the like.
Thefe are the more natural and lefs troublefome fvmptoms of gravidation, but this time is frequently attended with others more troublefome or hurtful, which art is able in fonie de- gree to mitigate. Seme are fubjeft to violent haemorrhages at the nofe, which are to be treated in the common way, and are ufua : ly as eafily cured as any other complaints .of that kind. In others the hemorrhoidal difcharges are very large during the time. Thefe are to be affwayed by giving pow- ders of nitre, cinnabar and crab's eyes, once or twice a day. Some are alfo fubjeft to an haemorrhage of the uterus itfelf, but this very rarely happens ; when it does it may be owing to two caufes, and therefore appear in two manners. In the
firit
