Method  of  tanning  Leather . 125 
but  thefe  liquors  are  not  only  troublefome  to  brew  and 
to  ferment,  but  they  are  always  uncertain  as  to  their 
degree  of  fournefs  or  ilrength,  which  depends  on  the 
ftate  of  the  weather,  and  other  variable  circutnftances ; 
thefe  liquors  are  moreover  exceedingly  apt  to  rot  the  lea- 
ther, and,  without  great  care,  may  injure  it  very  ma- 
terially in  its  texture. 
xvi.  To  obviate  thefe  inconveniences,  you  are  to  imi- 
tate the  bleachers  of  linen,  who  make  ufe  of  a four 
prepared  by  diluting  the  ftrong  fpirit  of  vitriol  (vulgarly, 
but  improperly,  termed  oil  of  vitriol)  with  a-  fufficient 
quantity  of  plain  water. 
xvii.  It  was  not  without  much  difficulty  that  the 
"bleachers  could  be  prevailed  on  to  quit  their  old  four- 
ings,  made  either  like  yours  of  rye  or  barley,  or  of  four1 
butter-milk,  from  a groundlefs  fear,  that  the  vitriolic 
fouring  would  corrode  their  cloth ; but  the  experience  of 
many  years  has  convinced  them  of  their  error,  and  now" 
no  other  fouring  is  ufed.  In  like  manner  the  tanners 
at  firft  may  fome  of  them  be  afraid  to  ufe  the  vitriol,  but 
a little  pradtice  will  ffiew  how  far  fuperior  this  fouring 
is  to  what  they  have  hitherto  ufed.  They  will  never 
find  it  fubjedt  to  any  change  in  refpedt  to  ftrength  from 
variations  of  weather,  or  different  degrees  of  heat;  and 
fob 
