Section forty-two of the Valuation Act, 1854, shall be read and construed as if the following proviso were inserted after the words " and all machinery fixed or attached to any lands or heritages, " that is to say: Provided that in any building occupied for any trade, business, or manufacturing process the expression " machinery fixed or attached " shall be construed as including all machinery, machines, or plant in or on the lands or heritages for producing or transmitting first motive power, or for heating or lighting such building, but save as herein provided shall not include machines, tools, or appliances which are only so fixed that they can be removed from their place without necessitating the removal of any part of the building.