In Prussia the working of certain mines is in the hands of the state, and was originally looked upon as an important contribution to the income of the state. As in the Dutch experience, the changes in production throughout the world have greatly reduced the returns and made the income variable; yet there is little disposition to dispose of these possessions. "The danger of mineral supplies being worked in a reckless and extravagant manner without regard to the welfare of future generations, and the dread of combinations by the producers of such commodities as tin, copper, and salt, with the aim of raising prices, have both tended to hinder the alienation of state mines."[7] The more common form of state monopoly is that which occupies a middle position, established for reasons of public safety or utility as well as of revenue. The salt monopoly enforced in Prussia was only abolished in 1867, and is still maintained in every canton of Switzerland. The strongest plea in its defense has been the guarantee by the state of the purity of the article sold, and this phase of the question has superseded the revenue aspect. Few articles of prime necessity, like salt, are subject to monopolies imposed by the state, and by a process of elimination it is only articles of luxury or voluntary consumption that are regarded as fit objects of monopoly for the benefit of the state. A tax imposed upon an article at a certain stage of its production or manufacture may enforce the expediency or necessity of a state monopoly. Where the supervision of the state agents must be so close as to interfere with the conduct of the industry, the state intervenes and itself controls the manufacture and sale. Tobacco has long been subject to this fiscal _régime_, and, proving so productive of revenue, there is little to be said against a monopoly by the state of its manufacture and sale. In Italy the tobacco monopoly is conceded to a company, but its return of net revenue to the state is nearly as large as the revenue derived from the taxes on real property (about thirty-eight million dollars a year). Prussia imposes a charge on the home-grown tobacco by a tax on the land devoted to its culture, but the return is very small, and Bismarck wished to introduce a true tobacco monopoly, modeled on that of France. But the conditions were opposed to his scheme, for the use of tobacco is general throughout the empire, and a proposition to increase its price by taxation or modify its free manufacture and distribution excited a widespread opposition. France maintains a full monopoly, and finds it too profitable to be lightly set aside unless some equally profitable source of revenue is discovered to make good the loss its abolition would involve.