The thinking mind can easily go one step further and imagine that, since the tar contains a number of volatile hydrocarbons, it might be made more adaptable for impregnation by paper by distilling it, as by this process the fluid would lose its tendency to evaporate and the percentage of resinous substances increase. Singular to say, there was a prejudice against the employment of distilled tar, entertained by builders and people who had no knowledge of chemistry. Increasing intelligence and altered business circumstances, however, brought about the almost universal employment of distilled tar, and every large factory uses it at present. The roofing paper prepared with distilled tar is perhaps most suitably called asphaltum paper, as this has been used in its manufacture. It possesses properties superior to the ordinary tar paper, one of which is that immediately after its manufacture, as soon as cold, it is dry and ready for shipment; nor does it require to be kept in store for a length of time, and it has also a good, firm body, being as flexible and tough as leather. It is very durable upon the roof, and remains flexible for a long time. It is true that asphaltum papers will always in a fresh state contain a small percentage of volatile ingredients, which after a while make it hard and friable upon the roof; but, by reason of its greater percentage of resinous components, it will always preserve a superior degree of durability and become far less porous. One hundred parts by weight absorb 140 or 150 parts by weight of coal tar. A factory which distilled a good standard tar for roofing paper recovered, besides benzole and naphtha, also about ten per cent. of creosote oil, used for one hundred parts raw paper, 176.4 partially distilled tar. Experiments on a larger as well as a smaller scale reduced this quantity to an average of 141.5 parts for one hundred parts raw paper. The weight of sanded paper is very variable, as it depends altogether upon the size of the sand grains. It may be stated generally that the weight of the sand is as large as that of the tarred paper.