sand-blast should not be used to clean new metal because it will remove the black oxide, or mill scale, which in itself, like paint, is a protection against rust formation so long as it remains. The sand-blast certainly offers the best means of cleaning old structures which are very rusty, and now that portable air compressors are available, it is fair to presume that metal coatings will have better opportunities in the future to prove the life that is in them than they have had in the past. For an interesting paper on sand-blast cleaning of steel, with discussions by prominent engineers, the reader is referred to the "Transactions of the  American  Society  of Civil Engineers," Vol. L., Paper No. 948.

It is said that a thousand times as much iron and steel is cleaned by pickling as is cleaned by  the sand-blast;  for example, all