proposing to "butt into" an
old-established industry, in which the principal manufacturers
were concerns of long standing. He appreciated fully its inherent
difficulties, not only in manufacture, but also in the marketing of the
product. These considerations, together with his long-settled principle
of striving always to make the best, induced him at the outset to study
methods of producing the highest quality of product. Thus he was led to
originate innovations in processes, some of which have been preserved
as trade secrets; but of the others there are two deserving special
notice--namely, the accuracy of mixing and the fineness of grinding.

In cement-making, generally speaking, cement rock and limestone in
the rough are mixed together in such relative quantities as may be
determined upon in advance by chemical analysis. In many plants this
mixture is made by barrow or load units, and may be more or less
accurate. Rule-of-thumb methods are never acceptable to Edison, and he
devised therefore a system of weighing each part of the mixture, so
that it would be correct to a pound, and, even at that, made the device
"fool-proof," for as he observed to one of his associates: "The man at
the scales might get to thinking of the other fellow's best girl, so
fifty or a hundred pounds of rock, more or less, wouldn't make much
difference to him." The Edison checking plan embraces two hoppers
suspended above two platform scales whose beams are electrically
connected with a hopper-closing device by means of needles dipping into
mercury cups. The scales are set according to the chemist's weighing
orders, and the material is fed into the scales from the hoppers. The
instant the beam tips, the connection is broken and the feed stops
instantly, thus rendering it impossible to introduce any more material
until the charge has been unloaded.

The fine grinding of cement clinker is distinctively Edisonian in
both origin and application. As has been already intimated, its author
followed a thorough course of reading on the subject long before
reaching the actual projection or installation of a plant, and he had
found all authorities to agree on one important point--namely, that the
value of cement depends upon the fineness to which it is ground. [16] He
also ascertained that in the trade the standard of fineness was that 75
per cent. of the whole mass would pass through a 200-mesh screen. Having
made some improvements in his grinding and