ANTISEPTIC TREATMENT OF WOOD. 521 



only i pint and less than half the amount of water 

 absorbed by red-gum. As street paving-blocks absorb 

 much ammonia and emit an offensive odour this process is 

 a sanitary one, as well as affording superior durability from 

 hardening. 



3. Suitability of d (if c rent W<*<nl for Injection. 



The species of woods are susceptible of impregnation in the 

 following order : 



The question as to the comparative ease or difficulty with 

 which a piece of wood can be injected and whether the injec- 

 tion is thorough, or merely superficial, cannot as yet be 

 answered satisfactorily. As a rule, a thorough injection is 

 rare; in most cases the antiseptic liquid injects merely the 

 sap wood and younger woody zones ; in the case of railway- 

 sleepers which are injected pneumatically, it also passes into 

 the two ends of the sleepers, whilst the heartwood in the centre 

 is often only partially injected. There are, however, many 

 modifications in the above condition of injected wood, accord- 

 ing to the species of wood, its soundness or unsound ness, 

 special anatomical structure and amount of contained resin, 

 which differs greatly in individual cases. 



The more resinous a wood the less easily it is injected, and 

 much resin in the wood may prevent injection entirely, as for 

 instance in pinewood ; it has not been ascertained whether 

 the different injecting processes affect matters in this respect. 



Beechwood with reddish false heartwood (from trees over 100 

 years old) is quite unsuitable for injection. It is not known yet 

 whether variations in the specific gravity of the same wood 



