Ellis, D. R. <br/><br/>
Hard and soft water :  part 1 / 
David Rhodes Ellis. 
 - Oxford :  Pergamon,  1970. 
 - A20, B20, [4] p. ;  11 x 17 cm. 
 - Pergamon practical programme,  3 .
<br/><br/><label>Subjects--Topical Terms: </label><br/>Water--Programmed instruction.