VALUATION  OF  ESSENCE  OF  MUSTARD. 
285 
Messrs.  Mellor  and  Co.,  of  Manchester.  The  last  operation 
■which  magnesium  has  to  undergo  before  it  reaches  the  hands 
of  the  photographer  consists  in  being  formed  into  wire. 
Owing  to  the  low  degree  of  ductility  possessed  by  magnesium 
this  is  a  matter  of  considerable  practical  difficulty,  as  it  cannot 
be  easily  drawn  in  the  ordinary  way  into  wire,  but  requires  to 
be  forced  through  small  apertures  into  a  steel  block,  the  metal 
being  kept  at  a  heat  below  redness,  at  which  point  it  is  much 
more  malleable  than  at  ordinary  temperatures.  On  this  point, 
however,  we  can  offer  but  little  precise  information,  as  the  best 
mode  of  magnesium  wire-making  is  kept  secret.  Magnesium, 
when  pure,  is  a  silver-white  metal,  of  specific  gravity  of  1-75.  It 
presents  a  crystalline  structure,  and  is  rather  brittle.  Its 
equivalent  is  12.  It  exhibits  much  chemical  analogy  to  zinc, 
but  for  certain  reasons  it  is  generally  classed  with  the  metals  of 
the  alkaline  earths.  It  melts  and  volatilizes  at  nearly  the  same 
temperature  as  zinc.  It  does  not  easily  oxidize  in  dry  air,  but 
if  moisture  be  present  it  is  rapidly  covered  with  a  film  of  hy- 
dra ted  oxide.  It  is  quickly  dissolved  by  diluted  sulphuric  acid 
with  formation  of  Epsom  salt.  When  thrown  on  a  little  very 
concentrated  hydrochloric  acid,  it  bursts  into  flame  for  an  in- 
stant. It  is  not  acted  on  by  a  mixture  of  concentrated  nitric 
and  sulphuric  acids.  It  burns  with  great  brilliancy  when  heated 
in  the  vapor  of  iodine  and  sulphur,  but  less  brightly  in  that  of 
bromine.    It  also  burns  in  chlorine. 
Professor  Roscoe  has  estimated  the  expenditure  of  magnesium 
at  ten  grains  for  each  portrait  taken  with  the  camera ;  but, 
even  with  the  chemicals  in  good  working  order,  this  may  be  con- 
sidered the  minimum  weight  of  metal  required  to  be  burnt.  In 
conclusion,  we  may  observe  that  the  steady  combustion  of  thick 
wires  of  magnesium  may  be  materially  facilitated  by  having  the 
wire  flattened  out  by  passing  between  heavy  rollers.  This 
"ribbon"  can  be  now  purchased,  and  it  burns  more  steadily 
and  can  be  ignited  more  easily  than  the  round  wires  at  present 
in  use  London  Pharm.  Jour.,  from  British  Journal  of  Pho- 
tography and  Medical  Press. 
VALUATION  OF  ESSENCE  OF  MUSTARD. 
Perfectly  pure  essence  of  mustard  dissolves  in  concentrated 
sulphuric  acid,  with  hardly  any  coloration;  but  the  oils  often 
