M O R 
32 
the draught being fo eafy.” This machine may be 
wrought by any other power, as water, wind, or Hearn. 
The falt-petre workers in France ufmg the mortar of 
old buildings for extra&ing that fait, M. Petit has thought 
it worthy a peculiar attention, and has made feveral trials, 
by way of analyfis of mortar, to determine whether it 
really and effentially contains nitre in it, or whether it be 
only ferviceable in that mixture of fajts from which nitre 
is produced. 
The common managers of the falt-petre works are of 
opinion, that mortar contains in it all the falt-petre they 
procure from it; and that the wood-allies, and other fub- 
llances they ufe with it, only ferve to abforb the fat or 
oily parts, and to fet the falt-petre at liberty to Ihoot. 
This they pretend to affirm upon experience; but they 
do not confider, that, though they can procure falt-petre 
from the rubbilh or mortar without the addition of wood- 
alhes, yet it is not pure mortar that they make their ex¬ 
periments upon, but fuch as is taken from theirown heaps, 
upon which they always throw all the refiduum of their 
former works, and all that liquor which will Ihoot no 
more cryltals, but which they call the mother-water of 
falt-petre. This gentleman, therefore, very properly 
judged, that to make a regular trial of the mortar or 
rubbilh alone, he mull not take it from their ftores, 
ufed in the falt-petre works, but pick it liimfelf from the 
ruins of old buildings. 
The mark the falt-petre workers have to know good 
mortar for their purpol’e is, that it talles acrid and fait 
when applied to the tongue; but to this it may be alfo 
added, that it ought to be of a greyilh colour, and fuch 
as, when powdered and fprinkled upon burning charcoal, 
yields fome fparks of lire; and the more fparks it gives, 
the better it is for the purpofe: and another charadler 
of the goodnefs is, that thefe well-impregnated mortars 
have a certain undluofity or fattinefs to the touch, which 
other kinds have not. 
The fineft of all kinds of mortar for falt-petre work is 
fuch as is had from the ruins of old buildings in a low 
fituation, and out of the way of much lun-lhine ; where 
there has been no great quantity of lire kept, and efpe- 
cially fuch as has ferved for the cements of the walls of 
ftables, or the like. M. Petit chofe from fuch a wall 
twelve pounds of old mortar; this he had beaten to 
powder, and poured upon it eighteen pints of water; the 
whole was then fet over the lire, and ftirred from time to 
time for three or four hours, that the water might be 
well tindlured from the mortar; after this the water was 
filtered through paper, and was then found to be tin&ured 
to a pale yellow tranfparent bitter, and lomewhat acrid 
to the taffe. 
The impregnation may be made without heat, by only 
flirring the mortar about for nine or ten days in cold 
•water; and the quantity of lalt taken up will be accord¬ 
ing to the goodnefs of the mortar and the quantity of 
water employed. The common fpecific gravity of this 
liquor to water is as 32 to 31, or thereabout. M. Petit, 
having procured the tindlure of fifty pounds of mortar, 
by feveral impregnations, in 72 French pints of water, 
evaporated it fo far till it appeared highly charged with 
faline particles, tailing very acrid and bitter, and being 
of a browniih-red colour; and its fpecific gravity was in 
this Hate to water as 4 to 3, there being more in quantity 
than about four pints. This was Hill limpid, and of a 
tlufky colour; and was afterwards evaporated over a gentle 
fire, to the confillence of an extradl, which, as it cooled, 
became much thicker and firmer, refembling butter. This, 
being left open to the air, loon relented into a liquor of 
the confillence of a fyrup: its fpecific gravity was now 
to water as 5 to 3 ; but, in leaving it open to the air, it 
continually attracted frefh humidity, and became lefs 
fpecifically heavy. Experiments made with this extradl 
fucceeded in the following manner: 
j. It turned the common blue paper to a fine deep red. 
TAR. 
The impregnations in water uninfpifiated do this alfo in 
different degrees, according to their ltrength. 
2. Mixed in equal quantities with fpirit of nitre and 
with fpirit of fea-l'alt, it made no effervefcence or altera¬ 
tion in either. 
3. A leaf of gold, being put into the mixture of this 
impregnation with fpirit of nitre, was immediately dif- 
folved; and, in an hour or two afterward, the liquor was 
much clearer than before. A leaf of gold, being put into 
the mixture of this impregnation and fpirit of fea-l'alt, 
was in the fame manner dilfolved in a few minutes. It 
is generally fuppofed, indeed, that the fpirit of fait alone 
will dilfolve gold; but there feems to be an error in this, 
founded on the inaccuracy of the preparation of fuch 
fpirit of fait; for Meflrs. Geoffroy and Boulduc have at 
different times produced before the French Academy 
fpirit of fait carefully prepared by themfelves, which 
would not at all diffolve gold, not even with the affillance 
of heat: even fuch fpirit of fait would, however, be made 
to diffolve gold, by mixing this impregnation with it; 
lo that it has the power of diffolving gold in a great 
degree. 
4. A leaf of filver being dilfolved in fpirit of nitre, and 
this impregnation of mortar added to the folution, the 
whole became turbid, and a precipitation happened, part of 
the matter being thrown to the bottom, and part remain¬ 
ing fufpended in form of a white cloud, which kept its 
place without falling. 
5. The impregnation being mixed in equal quantities 
with oil of vitriol formed a coagulum, and made a great 
effervefcence, with copious red vapours, and a ftrong 
fmell ol aqua fortis; and thefe vapours appeared at any 
time, on Itirring the mixture, for feveral days together. 
If a larger quantity of oil of vitriol be added to this coagu¬ 
lum, it all becomes fluid, but ferments violently; and 
finally, there will be a white matter precipitated to the 
bottom of the clear liquor; and, if a leaf of gold be 
brought near this mixture, it will be dilfolved even by 
the vapour which exhales from it. Spirit of nitre has no 
effefl upon this mixture, either in its Hate of coagulum, 
or when reduced by more oil of vitriol into a clear liquor; 
but the volatile fpirit of urine ferments violently, with¬ 
out the lead heat with it. 
6. Oil of tartar per deliquium being added to the im¬ 
pregnation, the liquors would not readily mix, but re¬ 
mained l'eparate, the impregnation linking to the bottom ; 
but, onffiring them thoroughly together, they finally were 
made to unite into a white l’ubllance like butter, with a 
ffrong urinous fmell. If a fmall quantity of corrofive 
iublimate be added to this mixture, the urinous fmell 
ceafes; and, if oil of vitriol be added, there is a violent 
fermentation occafioned; and, in fine, a large quantity 
of precipitate. 
7. This impregnation of mortar being mixed with an 
equal quantity of a folution of corrofive Iublimate, there 
is nothing remarkable produced, though the mixture be 
ever fo much fhaken; but, if a little oil of tartar per 
deliquium be added to this, the mixture becomes turbid, 
and, on Hirring all together for lome time, it becomes 
white and thick like butter. If to this, more corrofive 
Iublimate be added in folution, it becomes orange-co¬ 
loured : and, on more Hirring, this becomes again white; 
and finally gives a white precipitate at the bottom of a 
tranfparent liquor. 
8. If, inffeaa of oil of tartar, an equal quantity of lime- 
water be added, this in the fame manner gives an urinous 
fmell; and the whole difference is, that the mixture will 
not become thick with this, as it will with oil of tartar. 
9. The impregnation of mortar produced the fame 
coagulum in mixing with fpirit of urine, that it did with 
oil of tartar per deliquium; but it made no coagulation 
with fpirit of fal ammoniac with lime : the occafion of 
this difference is, that the fpirit of urine contains a great 
deal of volatile fait, and the other but little. It is a 
common 
