Two illustrations will throw light upon some of the demands which the wage earners frequently presented. Writing in August, 1886, Andrew Carnegie, the prominent steel manufacturer, discussed the proper length of the working day. Every ton of pig-iron made in the world, with the exception of that made in two establishments, he asserted, was made by men working twelve hours a day, with neither holiday nor Sunday the year round. Every two weeks it was the practice to change the day workers to the night shift and at that time the men labored twenty-four hours consecutively. Moreover, twelve to fifteen hours constituted a day's work in many other industries. Working hours for women and children had almost equally slight reference to their physical well-being. The "truck-system" was a less widespread abuse, but one that caused serious trouble at certain points. Under this plan, a corporation keeps a store at which employees are expected to trade, or are sometimes forced to do so. Obviously such a store might be operated to the great benefit of the workman and without loss to the employer, but the temptation to make an unfair profit and to keep the laborer always in debt to the company was very great. A congressional committee which investigated conditions in Pennsylvania in 1888 found that prices charged in company stores ran from ten per cent. to 160 per cent. higher than prices in other stores in the vicinity, and that a workman was more likely to keep his position if he traded with the company. The most insistent cause of industrial conflict was the question of wages. Forty-one per cent. of all the strikes between 1881 and 1900 were for more pay; twenty-six per cent., for shorter hours. Between the close of the war and the early nineties, industrial prosperity was widespread except for the period of prostration following 1873 and the less important depression of 1884. Not unnaturally the laborer desired to have a larger share of the product of his work. The individual, however, was impotent before a great corporation, when the wage-scale was being determined; hence workmen found it advantageous to combine and bargain collectively with their employer, in the expectation that he would hesitate to risk the loss of all his laboring force, whereas the loss of one or a few would be a matter of indifference.