Iie ye 
I nave faid that alkalies of the fame /pecves may thus be dire@lly 
compared, becaufe alkalies of diferent {pecies cannot, but require 
the intervention of another proportion ; and the reafon is, becaufe 
equal quantities of alkalies of different f{pecies precipitate unequal 
quantities of earth of allum. Thus too parts by weight of mere 
vegetable alkali precipitate 78 of earth of allum; but too parts 
of mznera/ alkali precipitate 170,8 parts of that earth. ‘Therefore 
the precipitation of 78 parts of earth of allum by vegetable alkali 
denotes as much of this, as the precipitation of 170,8 of that earth 
by the mineral alkali, denotes of the mineral alkali. Hence the 
quantities of alkali in all the different fpecies of pot afhes, pearl 
afhes, weed or wood afhes, may be immediately compared by the 
above teft, as they all contain the vegetable alkali, and the dif- 
ferent kinds of kelp or kelps manufactured in different places, 
and the different forts of barilha, may thus be compared, becaufe 
they all contain the mineral alkali; but kelps and pot afhes, as 
they contain different forts of alkali, can only be compared toge- 
ther by means of the proportion above indicated. 
THE application of this teft is founded on the following 
principles : 
tft, That a hot folution of a free alkali, or of an alkali com- 
bined only with fixed air or fulphur, can hold no terreno or 
metallico neutral {alt in folution, though it may alkalino neutra 
falts or quick lime, if the alkali be free from fixed air. 
edly, That earth of allum cannot be precipitated either totally 
or partially by the hot folutions of any alkalino neutral falt, and 
therefore that its precipitation is always due to the prefence of a 
D free 
