THE CORROSION OF IRON AND OTHER METALS 65; 



together, under the simplest possible conditions, the purest 

 obtainable water, oxygen and iron in vessels which would be 

 least likely to be acted on by any of these substances." 



Now, although it may be true that " to the pure all things 

 are pure," to the chemist who thinks all things are impure and 

 must ever remain so — some contamination is unavoidable; the 

 important question to consider is whether or no a particular 

 impurity can be counted as harmful. Pure is defined in the 

 dictionary as — " separate from all heterogeneous or extraneous 

 matter " ; a pure thing is the thing in itself. There can be no 

 degrees of purity — pure is to be qualified only by such words 

 as " nearly," " far from," etc. At most, we can speak of " highly 

 purified " or of " very nearly " or " all but pure " substances. 

 Messrs. Lambert and Thomson misuse and misapply the word 

 " pure " throughout their communication. 



The results they have obtained show, they say : 



" that chemically pure iron will not undergo visible oxida- 

 tion even after long exposure to pure water and pure oxygen 

 in vessels made of clear fused silica. Further, that a very 

 small trace of impurity in the iron is sufficient to cause 

 oxidation under exactly the same conditions, where there is 

 not the remotest chance of any acid substance either being 

 present or being formed during the reaction." 



It is worth while considering to what extent these statements 

 are justified. " Chemically pure," unfortunately, is a phrase to 

 which no precise meaning can be attached — it means a material 

 purified by a chemist, whose degree of success will depend on 

 the methods he may adopt in purifying the material. Messrs, 

 Lambert and Thomson tell us that to prepare " pure iron" they 

 took a " a pure specimen " of ferric chloride from a certain 

 dealer — at the best a very indefinite description. Metallic iron 

 was separated from the salt by electrolysing it between iridium 

 electrodes. The metal was then made into nitrate, the which 

 salt was purified by recrystallisation from purified nitric acid ; 

 the salt then obtained was colourless, whereas ferric nitrate 

 prepared from " ordinary pure iron " is pale violet ; this is pro- 

 bably the most interesting and valuable observation made in 

 the course of the inquiry and is alone well worth all the 

 trouble they expended on the preparation of the salt. Ulti- 

 mately the nitrate was decomposed by heat and the oxide 



43 



