﻿Chemistry 
  and 
  Physics. 
  79 
  

  

  SCIENTIFIC 
  INTELLIGENCE. 
  

  

  I. 
  Chemistry 
  and 
  Physics. 
  

  

  1. 
  The 
  Determination 
  of 
  the 
  Density 
  of 
  Solids. 
  — 
  Henry 
  Le 
  

   Chatelier 
  and 
  F. 
  Bogitch 
  observe 
  that 
  the 
  determination 
  of 
  the 
  

   specific 
  gravity 
  of 
  solids 
  is 
  one 
  of 
  the 
  simplest 
  of 
  physical 
  meas- 
  

   urements, 
  but 
  that 
  this 
  determination 
  is 
  usually 
  made 
  in 
  an 
  inex- 
  

   act 
  way, 
  so 
  that 
  it 
  is 
  unusual 
  that 
  the 
  density 
  of 
  a 
  solid 
  is 
  known 
  

   with 
  an 
  accuracy 
  of 
  one 
  part 
  in 
  100. 
  The 
  treatises 
  on 
  chemistry 
  

   hardly 
  ever 
  give 
  exact 
  numbers 
  for 
  densities. 
  For 
  example, 
  in 
  

   Moissan's 
  large 
  treatise 
  we 
  find 
  for 
  common 
  substances 
  occurring 
  

   frequently 
  in 
  a 
  state 
  of 
  great 
  purity 
  the 
  following 
  statements 
  in 
  

   regard 
  to 
  densities 
  : 
  

  

  Quartz, 
  between 
  2*55 
  and 
  2*74 
  

   Natural 
  galena, 
  varying 
  from 
  7*26 
  to 
  7*70 
  

   Artificial 
  galena, 
  varying 
  from 
  6*9 
  to 
  7*5 
  

   Natural 
  blende, 
  varying 
  from 
  3 
  "5 
  to 
  4*2. 
  

  

  Now, 
  in 
  regard 
  to 
  quartz, 
  deLepinay 
  and 
  Buisson 
  have 
  shown 
  

   that 
  its 
  specific 
  gravity 
  is 
  absolutely 
  fixed, 
  and 
  is 
  2*6507 
  with 
  an 
  

   uncertainty 
  of 
  only 
  one 
  unit 
  in 
  the 
  fourth 
  decimal. 
  

  

  The 
  authors 
  discuss 
  the 
  probable 
  cause 
  of 
  our 
  shocking 
  igno- 
  

   rance 
  in 
  connection 
  with 
  these 
  constants, 
  and 
  they 
  conclude 
  that 
  

   while 
  impure 
  substances 
  and 
  insufficient 
  weights 
  of 
  samples 
  may 
  

   sometimes 
  cause 
  errors, 
  the 
  principal 
  cause 
  of 
  inaccuracy 
  is 
  the 
  

   adhesion 
  of 
  a 
  thin 
  layer 
  of 
  air 
  to 
  the 
  surface 
  of 
  the 
  solid. 
  They 
  

   observe 
  that 
  this 
  effect 
  is 
  well 
  known 
  to 
  be 
  enormous, 
  as 
  in 
  the 
  

   " 
  flotation 
  " 
  processes 
  of 
  separating 
  sulphides 
  from 
  other 
  miner- 
  

   als. 
  Upon 
  experimenting 
  with 
  various 
  liquids, 
  they 
  have 
  found 
  

   that 
  carbon 
  tetrachloride, 
  benzol 
  and 
  petroleum 
  ether 
  do 
  not 
  

   give 
  this 
  difficulty, 
  and 
  they 
  recommend 
  that 
  water 
  should 
  never 
  

   be 
  employed 
  for 
  the 
  purpose. 
  They 
  have 
  devised 
  a 
  very 
  simple 
  

   and 
  convenient 
  apparatus 
  for 
  determining 
  specific 
  gravities. 
  It 
  

   consists 
  of 
  a 
  glass 
  tube 
  of 
  about 
  5 
  mm 
  interior 
  diameter, 
  graduated 
  

   in 
  cubic 
  centimeters 
  and 
  their 
  tenths, 
  with 
  a 
  bulb 
  at 
  its 
  lower 
  

   extremity 
  and 
  placed 
  upright. 
  The 
  tube 
  is 
  charged 
  with 
  the 
  

   liquid, 
  the 
  level 
  is 
  read, 
  either 
  by 
  the 
  eye 
  alone 
  or 
  by 
  means 
  of 
  a 
  

   cathetometer, 
  and 
  the 
  weighed 
  solid, 
  thoroughly 
  freed 
  from 
  dust 
  

   by 
  sifting, 
  is 
  introduced 
  by 
  means 
  of 
  a 
  long 
  funnel. 
  The 
  increase 
  

   in 
  volume, 
  which 
  should 
  amount 
  to 
  at 
  least 
  about 
  3 
  CC 
  , 
  is 
  deter- 
  

   mined 
  by 
  reading 
  the 
  new 
  level 
  of 
  the 
  liquid. 
  Using 
  carbon 
  

   tetrachloride, 
  with 
  coarse 
  and 
  fine 
  material 
  in 
  each 
  case, 
  galena 
  

   gave 
  the 
  results 
  7*584 
  and 
  7590, 
  while 
  zinc 
  blende 
  gave 
  4*079 
  

   and 
  4*079. 
  When 
  water 
  was 
  employed, 
  even 
  in 
  cases 
  where 
  it 
  

   was 
  attempted 
  to 
  remove 
  the 
  adhering 
  air 
  by 
  exhausting 
  the 
  air 
  

   above 
  the 
  liquid, 
  the 
  results 
  were 
  very 
  unsatisfactory. 
  — 
  Comptes 
  

   JRendus, 
  clxv, 
  459. 
  h. 
  l, 
  w. 
  

  

  