A Course of Experiments to Ascertain the Specific Buoyancy of Cork in Different Waters: The Respective Weights and Buoyancy of Salt Water and Fresh Water: And for Determining the Exact

A Course of Experiments to Ascertain the Specific Buoyancy of Cork in Different Waters:The Respective Weights and Buoyancy of Salt Water and Fresh Water: And for Determiningthe Exact Weight of Human and Other Bodies in Fluids. By John Wilkinson, M. D. F. R. S. ofLondon and GottingenAuthor(s): John WilkinsonSource: Philosophical Transactions (1683-1775), Vol. 55 (1765), pp. 95-105Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/105451 .

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[ 95 ] zI45 Teucrium foliis ovatis acute incifoSerratis gla-

lzris, florlbus axillaribus geminis caule, eredo. Linn. Sp. plant. 790.

2 1 46 Tithytnalus Linaria folic lunato flore. Mor. H. Reg. BleE.

2147. Valeriana fylveRris major altera, fol. lucido. ES. Reg. Par.

ZI48. Veratrunl racemo compof1to) corollis paten- tiffilmis. Linn. Sp. pJant. I479.

2I49 Veronica racemis lateralibus, foliis lineari lan- ceolatis pinnato dentatis. Linn. Sp. plant I7.

2 I so Volkatneria ramis inermibus. Linn. Zeyl. s3 1.

XVI. iC Coarye of Experuanents to vfcertain the Specific BuoyanCy of Cork in diyerrt ZYaters: lJhe re§<peSive EYeights ard Baoy- ancy of Salt Zater and FreJh tYater * Alndfor detertninzng the exaS EYeight of Human and other Bodies io% Fluids. By John WilkinSon, M. D. F. R. S. of TJondon and Gottingen.

CExperazenfs fo defermine the Specifc Bvoyancy of Cork in River lYaZer*]

Experilnent I. Pitad Nlarch t4 C I X cubes .of good cork, every one

1765 J meafiuring an incll rquaref as nearly

as they could poilbly be aScertained, with a gra- duated

[ 95 ] zI45 Teucrium foliis ovatis acute incifoSerratis gla-

lzris, florlbus axillaribus geminis caule, eredo. Linn. Sp. plant. 790.

2 1 46 Tithytnalus Linaria folic lunato flore. Mor. H. Reg. BleE.

2147. Valeriana fylveRris major altera, fol. lucido. ES. Reg. Par.

ZI48. Veratrunl racemo compof1to) corollis paten- tiffilmis. Linn. Sp. pJant. I479.

2I49 Veronica racemis lateralibus, foliis lineari lan- ceolatis pinnato dentatis. Linn. Sp. plant I7.

2 I so Volkatneria ramis inermibus. Linn. Zeyl. s3 1.

XVI. iC Coarye of Experuanents to vfcertain the Specific BuoyanCy of Cork in diyerrt ZYaters: lJhe re§<peSive EYeights ard Baoy- ancy of Salt Zater and FreJh tYater * Alndfor detertninzng the exaS EYeight of Human and other Bodies io% Fluids. By John WilkinSon, M. D. F. R. S. of TJondon and Gottingen.

CExperazenfs fo defermine the Specifc Bvoyancy of Cork in River lYaZer*]

Experilnent I. Pitad Nlarch t4 C I X cubes .of good cork, every one

1765 J meafiuring an incll rquaref as nearly

as they could poilbly be aScertained, with a gra- duated



[ 96 ]

duBed gag of rk fallened to a point fif eacht iFeZ verally weighed as follows;

Grains N° l 49

2 47t 3 47 4 46 w

5 46 6 43

Sum of Weights 279 1 Grains-

the medium weight, being the exa& welght of-acubic inch of cork is 46 6T.

Experiment II.

N° , 2 3, 4, formed a floatrxamed A, being I90

grains of cork, which was faRened to a medxllion of lead, weighing two ounces, by a wire that weighed eight grains; thefe being put into a deep jar of Thames water,- taken above the new bridge, the lead weigh^<d exaftly 44 grains fo that I90 grains of cork fispported precsSely gs6 grains of lead in river water.

Experiment III.

The+fltat was left in the ranze water) immerSed by the medallion for the fpace of 48 hours) with a riew of obtaining a precire knowledge of the quantity of water the cork ulight -imblbe; how its butyancy might be affedved; and how much extenfion it might acquire from a certain continuance under tlle water

2 It



[ 97 ] It was fomewhat furpriGng to find, that aftr this

period of immerl;on the cork had nota as might have been expeded, loft any brce of buoyatlcy; but Otl t;he contrary, it had aflcLlally gained two grains, and was follnd to fupport 918 grains of lead: which muIR be attributed, it may be prefumed, to an ex- panf1orl of tIze air contained in the cork, acquired from it$ imawerrlon in the frefh water

To be fiurther informed how cork s{-ould be affedred lJy a continued immerfion, the fame float, after nveighing, was again immerSed in the fame water, for the fipace of 48 hours longer. And now the water was found to have penetrated its receSes and cavities, in fo rullch that its buoyancy had decreafed I I grains, and it then only fupported gos grains This decreaGe anay poffilbly be attributed to a greater imbibition in the c-ork, and a greater penetration giverl to the water, by its having been now 96 hours in a chamlter, with a'fire in it, by whith it might be warmed. This float A being taken out of the water, wiped, and tatd in a dry place fUr z4 hours, weighed 2 I I grains, having gained by abSorption S X grains of additional weight.

Experiment IV The float, in« this Ilate, having been z4 hours out

of the fie{h water, was now plit into falt svater brought from the North Foreland, in which it was found to fupport the sveigllt of 954 grains, of a lead-en medallion, having ehe power of buoying up 38 grains more in ehe fea water) than it did in the river water, svith vvhich it was nearly faturated at the time of its immerfion in the Sea water.

VOL. LV. O After



[ 98 ] After an immerfiQn of 48 hours in- the filt water,

this float (A) lok 1 6 grains of its buoyant power-; and having been 7a hours in the falt water, upon weighing of it again out of the water, being wiped} but filll of water? it was found to weigh Z4I grains) having gained 30 grains After being nine hours out afthe water, in a dry rxm, it weighed a13 grains, having loIt 28 grains. This float (A) having been 76 hours in the falt water) in whicll it then fuIlained -g4g grains of lead was realoved, thus liturated with the fea water, into a veGel of freXh river water and was found to [uRain 923 grains only, being 26 grains lefi than it bore up- in the iAlt water; and yet it muR be obirved, that this float had been fa- turaed wi:th filh water before it was immerfed in the fiIt water Experitnenh made a ver the Sp.cR Bt s tf

Cork in Salt er. Exzriment V.

Not content merely to know the buoyant power sof cak in fFeM water it was next tried in fea water Four cubes, being each an inch I4uare on every flde, made of the beflc found compad cork with diRinA gages made of cork} and aNoining, as in the pre- ceding experiments, were preparedX each weighing as fUllows ; :

Grains N° I 42

2 42 X

3 54 + 53 5 43

Amountint,, in a11 to 234 . Grains. theSe



[ 99 ] thefe belng united- formed one float (marked B) that they might the nearer reSeml)le the texture of the cork jacket. A veSel of Sea water take-n up near the Notth Foreland being then provided, the float was found to fupport in it a leaden medallion weighing Io48 grains. Wben it had continued in the fea water for 48 hours,- it exadrly fupported X o24 grains, having, by being in the falt water} for that Epace of time, loR -Z4 grains of its lJuoyant power.

From this expeliment we learn, thae-the falt water infirluates more into-the fubIlance of cork:than freth water doth, which may perhaps be attributed to its oilynefs, * oil besng, as is very well known, more fubtil and penetrating, than water; it could not therefore be expedted that ehe cork {hould therein retain its force to vigorouily, for fo long a time, as it doth in the freXh risrer water; and, on weigh-

ing, it was foulld to loSe of iftsV buoyancy in 48

hours. But then we are falrther to obServe from the above,

that the Sea water fuppores a greater weight, and gives more buoyancy to the cork float than freSh waterf in the proportion of 3 53 to 3 59 ; for a float weighing 44 grains, fupporting 353 grains of lead in freh water, buoyed up 3 59 grains of lead in the fea svater) being more by fix grains And it is tobe noted, that the fea water taken up at the North Foreland is not fO much impregnated with the- nzariIle principles, as that which is taken up at a greater diItance from fieXh water rivers, which decreaSes in its buoyancy in

* Vid. WIacellinlls. - Pliny (Lib. xxxi. Cap. 7.) P. Bour>es (Lett. Miffilonaires, O&av. Edit.) and lDr. Hales.

O 2 propor-



[ too ]

proyortion to its vicgnity to or mixture xvith rivers 3 fiAr n evaporating it yielded only tero drachms and one

grain of falt to a pint svhich is lets by Seven grains than is yielded by that taken up at the InC of Wight.

Experiment VI

The float B ing continued in immerElon it] {i1t water for 7s hours it had 1oR 26-grains nzere of its buoyant force, lofing in the firil 48 hours 24, aad in the 24 fucceedillg hours two grains c:nly; from hich it appears, that) after the cork has been in the water for 48 hours, lts abSorption becomes lefs than -befbre, in proportion as I.2 iS to I.;

This float havirg continued in the water for 78 hours, each piece of cork, being vriped very dry on its furfacea butnot Squeesed, weighed asfollows;

° I weiglled 55 X Grains havong gained I 2 Grains -2 47 43

3 66 I2

4 5 9 T 5 z 5 5I o 8 >

_ __

Ail S weigh, s79^1 gained 42

............................. ..

.

Being then defirous to knossr if any quantity of falt had infinuated into the pores of the cork, and if fo, how much; the alDove float vZas hung up to dry ln a warm airy room) svhere it uras not far from th-e fire, f-or the fipace of 48 hours > v?hen it feemed to

bt



[ ttt ] be qvxite dry, and each piece bexng weighed, was found as follows;

Gr. Gr Nt X weighed 45 the AIt Xppofed to be contained was 3

2 46 3t- 3 59 6

4 55 2

5 44 : 1 _ __ _

Ali 5 vveigh. z49 faIt gained 15-2 _ _

* . ., . ";

But on their- being hung near a fire for 72 hours, until perfedtly dry, no falt appeared to be imbibed, for the above numbers weighed as follows; having loR by extraordinary dryneSs about YI^th: Of their firR veight.

N° I weighed 40 Grains, having loR z Grains :2 42 - 4 3 54 3 4 :53 3 5 43 3

, _ _

_2 I

: Experialent VlI. For the fake of the greater exfadtneSs, another float

(marked C) was made of two cubes of cork;, amount- ing to I 64 grains; the larger Il 8, and the fmaller 46 grains; this was put into the fame veffiel of river water, after it had been 96 hours- in a warm cham_ ber, and fupported a medallion of lead weighing 766 grains; :it was left in the water for 36 hours longer, and weighed again, svhen it zras fbund to fspport 754 grains, having loIt I2 grains of its btloyant force in that fipace of immerfion. E;rom this iRecond experiment does it not appear, that this lofs

of



[ I02 ]

of buoyancy was prillcipally owing to the warmth the water had got by Itandin'g in a warm roonl, as was hinted at before, ̂hich was further proved by the thermometer ?

Two other floats, of 44 grains of cork each, having been 72 hours in river water, weighed each 53 grains, having gained nine grawns by the immerfion. Being laid to dry for s4 hours after, weiglled 46 grains, having relinquilhed feven grains each.

The float C, being wiped and put into a dry place for >4 hours, Vw'2S found to weigh I 83 grains, having gained I9 grains c)f weight. Tke float, in this Itate, was then immerSed in falt water, arld was found to fupport 864 grain-s, being I 10 grains more than it fupported in frelh water, after it had been faturated therewith; C, beingleft in faltwater48 hours, was, upon weighing, found to have loft fix grains of its buoyant power. Thts float C, having been 7z hours immerfied in the Sea water, was found, after being well wiped, to weigh 203 grains, having increafed in weight so grains by immerf1on. After being nine hours out of the falt water it was found to weigh

8$ grains, having lolt in that time 1 5 grains.

Experiment VIII.

A medal of lead, weighing -one drachm when out of the water, was found, on being weighed in river water, tobe 54 grains andahalf;^beingleSsbyfive grains and a half than out of the - water. The fame medal being weighed in the falt water tras found to weigh 53 grains and a half. Tile diffierence between its hydroftatical weights being preciSely one graiIz, or 5xTth more in river water tban in Sea sva;ter.

Expe



[ I03 ]

Experitnent IX. A pllial of river water weighed exaftly 82 grains;

the fame veSel of Sea water weaghed exad:ly 84; the dilErence was two gralns, or as 4I to 4z.

Under a11 thefe experilinents, theIe cubes of cork did not feenl to have gained any meafiurable extenfion; yet it is certain the volume of cork, like moI other fubIlances) svill alter by the imbibition of hunlidity.

Tlle ailirtion which has commonly been advanced, that the bodies of me;w in general are fpecifically lighter than their refipedive volumes of water, is not quite perfEdcly fbunded in truth; accunate experi- nlents, milutely obServed, will fatisfiEtorily evince the contrary to be true. Weighing hydroflically the lluman body canluot be fO precilely perfbrmed, as to permit us to drasv any certain infErence them- from, as eviclently appears from the insperfiEt at- tempts ssrhich the ingenious Mr John Robinfon made fUr tllat purpofe (SeSe Philofophical Tranfadr. Vol Lv Part II. Page 3o); on perufing of wllich, and the autllor?s ingenuous cotlfison of the inaccuracy of his experiments) it occurred, that a more concife and eat method of obtaining a certainty in this parw ticular, might perhaps attend the fUllowing attempt to diScover the fipecific gravity of the human body in svater.

Experiment X Affer }zaving mades the bregoing experiments,

utith a view of aScertasning tlze Ipectfic buoyancy of cork, and ali the alteration it might undergo from lreing immerfed in ris?er or fea water, we proceeded tn tile more important exarnen, to diScover the pre- ciic quantity of cork necefEry to iflcain a man in the

water



[ IO4 ] water. For this end, 22 pieces of t'ne beR cork} falch as is direded to be uSed for the jackets, * were provided; thefe were of (lifferent weights, from one ounce down to one Scruple; fO that by tneans of a firing to svhich they were occafionalJy filtened, one might eaf1ly learn what weight they would [uEpend in the water, and what sreight they would not fufpend. Tbis being done, the next buEenefs was to find a proper perSon to make the experitnent upon; for the acctaracy of which it was judgetl proper to ileEt a man of tile fmalSer fixe (as our Ie;zmen are feldom large) that was not very fat, becaufie fat people are mc)re buoyant than lean or bony perfons; one that could fwim, that he might go through the experiment with propriety, and withotlt fear; one, therefore, was fixed upon, who was plump and muScular, not rery bonyX but moderately fO;

His lleigllt was five fioet two inches; His svaiR mealured two feet ten inclles ;! His weight was one hundred and four pounds.

Thus fitted out, he Ilripped naked, and ten ollnces of cork beingtied about his neck and l)rea{t, he colnmieted 11imfelf to the river 'hames, near C jelfea, in a place where elle water sstas about a foot below his depth^; but hW could not keep his head abosJe the fllrface without employing his art, though he found not much art required to do it: anotller ounce of cork w>as tlzerefore added, and he pelceived himSelf raifed thereby, fo as now to be the tnore able tc) keep hi,naielf above tlle water, but yeg he went nowly to the bottotn, unleSs he took care by fwi.mming to pre- sent it. For tnis reafon anotl.er <:unce of cork was

* Tho C3rk ac'sets propoid for flving the lives of feawnen a+.<u otbc!s in thipwreck are here meant.

* a;pl-e



- w

' Ios

applied, but ilill he funk, though more ilowly than before; and it was plain to be obServed, that the point between that manner of flnlring and fwimtning vras balanced wih juch extrenze- nicety, tha-t ti fnallell addition of cork would determine in favour of buoyancy: accordingly half an ounce was added, and this weight fupported him in a vibrating Ibte; but by the fuper^addition of one drachm and t^o fcruples more of cork, he found himfelf very able to keep above water, in a living pofition, without any help from-his art of fwimming, and that it required fome fmall pains to inz1nerSe himfelf. It therefore refults fron1 this experiment, that twelve ounces, five drachms, and two Scruples, or 6IOO grains of cork, fupported tIzis man in river water; 6IOO grains of cork art equal tO I 63 °7 cubic inches ;. which appears, by a catculate drawn from the fecond of the foregoing expeximents, to be able to fupport 63 ounces, five drachms, and eight grains of lead, rhich mui} be, therefore, tlze exaflc weiglat of this man in river water By comparin-g this calculation with the above experiment IV. made in tlle fea water, we Ihall find that this luan weighed 6-o ounces, three drachms, and 2 r

grains; or four pounds, s z ounces, three drachmss and ZI grgins, requiring I2, ounces and 2I grains

of cork to i-upport him, in fea water. It muR how- ever be obServed, as we have already intimated, that the fame quantity of cork which Iupports a fiat, or very plump pellon, in the water, will not fufiice to buoy up a lean perXn, although their weights, out of the watera lDe equal.

VOL. EV. p XV1I.



Documents

A Course of Experiments to Ascertain the Specific Buoyancy of Cork in Different Waters: The Respective Weights and Buoyancy of Salt Water and Fresh Water: And for Determining the Exact