THE ZINC CREOSOTE PROCESSES.
The Rutgers, Card, and Allardyce Processes make use of zinc chloride and creosote. The first-named antiseptic is used because it is cheap, and the last is used because, in addition to its intrinsic value, it retards the escape of the zinc chloride. The two preservatives are forced into the wood while mixed together in the form of an emulsion, or they are introduced separately one after the other.
In the Rutgers Process, the zinc and creosote are introduced while mixed means that resemble those employed to introduce pure creosote during the Bethen Process. In Ger many, where every attention is paid to detail, the Rutgers Pro cess has caused pine ties to last for from fifteen to eighteen years. The process has been practiced successfully for about forty years.
The Card Process differs from the Rutgers Process in the means used to mingle the antiseptic liquids. These are first mixed together by forcing air through perforated pipes located at the bottoms of the mixing tanks; the agitation is then continued by means of centrifugal pumps. Further details resemble those followed in the Bethell Process. The best results are obtained with air-seasoned woods.
The Allardyce Process is planned so that the preservatives are introduced separately one after the other. First, a solution of zinc chloride is introduced into the wood by an air pressure of about 130 pounds per square inch. The cylinder is then drained and is refilled with creosote which is finally subjected to a pres sure of about 180 pounds per square inch. The penetration of creosote is not great and the process itself is not extensively used at the present time.