“ It is not material that such profit is taxed, along with other gains, under the general income tax law, for Congress has power to impose an increased or additional tax if satisfied there is need therefor. ”

“ The taxing provision does not impose a tax in respect of all transfers, but only in respect of such as yield a profit over cost and allowed expenses. If there be no profit, there is to be no tax. If there be a profit, the tax is to be 50 per cent. ”

“ The Silver Purchase Act, in section 8, imposes on all transfers of any interest in silver bullion, where the price for which such interest is transferred exceeds the total cost and allowed expenses, a tax of 50 per centum of such excess, and requires that the tax be paid by affixing to a memorandum of the sale lawful stamps in the amount of the tax. ”