4.--BLUE AND VIOLET DYES. Heat some of the paper with dilute spirit. If the alcohol remains colourless, we have Prussian blue or ultramarine. If it becomes blue or violet, shake some of the paper with concentrated sulphuric acid. A dirty olive green shows methylene blue, and a brownish colour shows spirit blue, water blue, Victoria blue, methyl violet, etc. If the spirit turns yellow, and the colour of the paper changes, we have wood blue or wood violet. CHAPTER XI PAPER MILL MACHINERY In the case of common printings and writings, which form the great bulk of the paper made, the possibility of one mill competing against another, apart from the important factor of the cost of freight, coal, and labour, is almost entirely determined by the economy resulting from the introduction of modern machinery. The equipment of an up-to-date paper mill, therefore, comprises all the latest devices for the efficient handling of large quantities of raw material, the economical production of steam, and the minimum consumption of coal, matters which are of course common to most industrial operations, together with the special machinery peculiar to the manufacture of paper. The amount of material to be handled may be seen from the table on page 215, which gives the approximate quantities for the weekly output of a common news and a good printing paper. _Economy in Coal Consumption._--The reduction to a minimum of the amount of coal required for a ton of paper has been brought about by the use of appliances for the better and more regular combustion of the coal, such as mechanical stokers, forced and induced draught, the introduction of methods for utilising waste heat in flue gases by economisers, and the waste heat in exhaust steam and condensed water by feed-water heaters, the adoption of machines for securing the whole energy of the live steam by means of superheaters, adequate insulation of steam mains and pipes, high pressure boilers, and engines of most recent design. The firing of steam boilers is now conducted on scientific principles, the coal being submitted regularly to proper analysis for calorific value, the evaporative power of the boilers being determined at intervals by adequate trials, the condition of the waste flue gases being automatically TABLE SHOWING THE MATERIALS REQUIRED FOR NEWS AND PRINTINGS.