182 
VARIETIES. 
Pyrolignite  of  Iron. 
In  the  proportions  adopted  by  the  writer,  viz  :  1  part  of  pyrolignite  to  6  parts 
of  water — cost  of  pyrolignite  23  cents  per  gallon. 
Labor  at  tank,  &c,  1-0  cent. 
Solution  absorbed,  6-5 
Cost  per  sill,  7-5 
The  writer  does  not  claim  that  this  method  of  impregnating  timber  by 
capillary  attraction  is  superior  to  any  process  extant,  for  such  an  assump- 
tion at  this  period  would  certainly  be  premature  and  somewhat  arrogant. 
The  question  of  its  efficacy  hangs  upon  a  single  point,  which  is  this.  Does 
it  introduce  a  sufficient  quantity  of  the  preservative  solutions  to  produce  the 
desired  effect?  From  the  mass  of  data  condensed  in  the  tables  given  above, 
it  appears  that  the  average  degree  of  absorption  varies  in  the  different  clas- 
ses of  woods.  The  average  of  the  sills  impregnated  in  the  tanks  range 
from  0-52*  to  0*78*  of  a  gallon  per  cubic  foot.  The  averages  of  the  timbers 
in  the  cistern  from  0-53*  to  1-10*  of  a  gallon  per  cubic  foot. 
In  the  interesting  account  of  the  Burnettizing  establishment,  at  Gloucester, 
England,  carried  on  under  the  direction  of  J.  K.  Brunei,  Esq.,  C.  E.,  pub- 
lished by  J.  B.  Francis,  Esq.,  it  is  stated  in  the  course  of  describing  the 
operation  of  the  apparatus,  that  in  a  partial  vacuum,  a  pressure  of  120  lbs. 
to  the  square  inch  is  maintained  from  two  to  four  hours  until  '6+  of  a  gal- 
lon of  the  solution  is  forced  into  each  cubic  foot  of  timber,  and  this  amount 
is  deemed  sufficient.  With  this  favorable  and  reliable  ovidence,  the  writer 
is  sustained  in  the  opinion  that  capillary  attraction  can  be  advantageously 
employed  as  the  agent  of  introducing  preservative  solutions  into  railway 
timber.  Its  chief  merit  rests  on  the  simplicity  of  its  requirements  in  the 
outset,  and  the  economy  of  labor  in  its  use. 
Dr.  Smith's  Sepometer. — Among  the  many  things  which  have  troubled 
the  minds  of  ordinary  thinkers  has  been  the  assertion  of  chemists  that  the 
air  had  in  all  places  the  same  composition.  We  cannot,  therefore,  be  suf- 
ficiently thankful  to  Dr.  R.  A.  Smith,  of  Manchester,  for  his  discovery  of 
an  instrument  by  means  of  which  we  can  ascertain  the  causes  of  the  dif- 
ferent degrees  of  purity  of  air.  As,  by  means  of  this  instrument,  the  ac- 
tual amount  of  putrescible  matter  in  the  air  can  be  measured,  Dr.  Smith 
has  given  to  it  the  name  of  "  Sepometer."  The  salt  he  uses  as  a  measurer 
of  impurity  is  almost  the  best  oxidizing  agent  with  which  chemists  are  fa- 
miliar ;  it  is  the  permanganate  of  soda.  The  process  consists  simply  in 
ascertaining  how  much  of  the  permanganate  is  decomposed  by  a  given 
amount  of  air.  The  indications  are  very  beautiful,  and  exhibit  the  great- 
est difference  between  the  air  of  towns,  country,  and  sea.  The  use  of  blood 
by  Dr.  Smith  is  also  novel.  By  means  of  the  smallest  quantity,  we  can  al- 
most instantly  ascertain  the  difference  between  town  and  sea  air,  by  sha- 
king it  with  a  small  portion  of  blood  in  a  tube.  We  shall  be  most  anxious 
•American  Gallons. 
