Any board of county commissioners may establish by resolution a cumulative reserve fund in general terms for several different county purposes as well as for a very specific county purpose, including that of buying any specified supplies, material or equipment, or the construction, alteration or repair of any public building or work, or the making of any public improvement. The resolution shall designate the fund as “cumulative reserve fund for . . . . . . (naming the purpose or purposes for which the fund is to be accumulated and expended).” The moneys in said fund may be allowed to accumulate from year to year until the board of county commissioners of the county shall determine to expend the moneys in the fund for the purpose or purposes specified: PROVIDED, That any moneys in said fund shall never be expended for any other purpose or purposes than those specified, without an approving vote by a majority of the electors of the county at a general or special election to allow other specified uses to be made of said fund.