Among the numerous industrial establishments in Boulogne and its environs may be mentioned foundries, cement-factories, important steelpen manufactories, oil-works, dye-works, fish-curing works, flax-mills, saw-mills, and manufactories of cloth, fireproof ware, chocolate, boots and shoes, and soap. Shipbuilding is also carried on.
Of fireproof material, 2 or 4 in.
From it have been transferred to the fireproof building of the Registry of Deeds many interesting historical documents, among them the records of the Plymouth colony, the will of Myles Standish, and the original patent.
The steel reinforcement is of immense importance in fireproof work, because, if properly designed, it enables the concrete to hold together and do its work even when it has been cracked by fire and water.
It contains, in addition to the ancient national records, adequate accommodation, in fireproof chambers, for all Scottish title-deeds, entails, contracts and mortgages, and for general statistics, including those of births, deaths and marriages.
At one time Portland cement concrete was considered to be lacking in fireproof qualities, but now it is regarded as one of the best fire-resisting materials known.
But they are weak, and modern experience goes to show that a strong concrete is the best, and that probably materials like broken clamp bricks or burnt clay, which are porous and yet strong, are far better than cinders as a fireproof aggregate.