344 
ADVANTAGES  OF  TWADDLE'S  AREOMETER. 
every  increase  of  density  equal  to  5  unities  is  represented  by, 
degree ;  thus — 
1°  Twaddle  =1-005 
2°  =1-010 
1°  =1-035 
The  degree  has  consequently  only  to  be  multiplied  by  5,  and 
the  number  thus  obtained  added  to  1-000,  and  we  obtain  the 
specific  gravity  of  the  fluid  under  examination. 
Hence  it  follows  that  this  areometer  is  one  with  a  rational 
scale  and  a  further  consequence  is  that  the  degrees  must  be  of 
unequal  length. 
That  the  employment  of  this  instrument  would  essentially  sim- 
plify some  calculations  is  evident  from  the  following : — 
1.  A  gallon  (English)  of  distilled  water  weighs  10  lbs.  (English). 
By  sinking  Twaddle's  instrument  into  a  solution,  an  acid,  &c, 
and  multiplying  the  degree  obtained  by  5,  we  readily  learn  the 
weight  of  a  gallon  of  the  latter  fluid.  For  instance,  an  acid  of 
50°  Twaddle  has  the  spec.  grav.  1-250,  and  the  gallon  consequent- 
ly weighs  12 1  lbs. ;  the  gallon  of  another  of  5°  Twaddle  weighs 
only  10J  lbs/ 
2.  With  French  measures  and  weights,  the  matter  becomes 
still  more  simple;  1  litre  of  distilled  water  weighs  1000  grms; 
1  litre  of  a  fluid,  say  of  20°  Twaddle,  therefore  weighs  1100  grms., 
I  e.  1000+20x5  grms. 
3.  If  an  acid  or  solution  of  a  given  degree  is  to  be  diluted  to  a 
lower  strength,  how  much  water  must  be  employed.  For  instance, 
sulphuric  acid  of  170°  Twaddle  is  to  be  diluted  to  6°.  The  pro- 
portion for  dilution  is  obtained  by  the  division  of  170  by  6 ;  the 
quotient  is  28-333 ;  that  is  to  say,  when  1  litre  of  acid  of  170° 
Twaddle  is  diluted  to  28.333  litres,  or  in  other  words  when 
27-233  litres  of  water  are  added  to  it,  we  obtain  a  fluid  of  6° 
Twaddle,  for  170°  Twaddle  represents  the  spec.  grav.  1-850  and 
6°  Twaddle,  the  spec.  grav.  1-030,  consequently  the  28-333  litres 
contain  27-333  litres  of  water,  1  litre  of  sulphuric  acid  weighing 
1-850  grm. ;  the  weight  of  the  whole  is  27-333  +1-850  grm.= 
29-183  grms. ;  hence,  by  dividing  the  total  weight,  29-183  grms., 
by  the  volume,  28-333  litres,  we  obtain  the  spec.  grav.  1-030. 
If  it  were  desired  to  perform  a  similar  calculation  with  the 
