At a time when market interest rates have soared to levels never before reached in this country, rates on deposits at banks and other financial institutions have been held much lower. The rate commercial banks charge on prime business loans has been 8 1/2 per cent since early last June. Mortgage and many other market interest rates are currently about as high. On the other hand, payment of interest is prohibited on demand deposits, and the maximum rates permitted on time and savings deposits vary between 4.50 and 7.50 per cent. The highest rate applies only to deposits in denominations of $100,000 or more maturing in a year or longer.