PART V.—SUMMARY OF PARTS I, II, IlI, AND IV, AND CON- 
CLUSIONS. 
PART I. FREE LIME IN PORTLAND CEMENT. 
(1) A method for determining the approximate amount of 
free lime and for distinguishing between sintered, nonsintered, 
and slaked lime is described. 
(2) The application of this test gave conclusive proofs of the 
presence and the effects of free lime in all the commercial Port- 
land cements examined, and a study of this free lime under 
different conditions of burning, grinding, and seasoning showed 
the following results: 
A. The degree of burning: 
(a) As the kiln temperature increases, nonsintered calcium oxide 
gradually becomes converted into a sintered state having 
different physical properties. 
(b) This conversion may occur at temperatures far below those 
necessary for the proper burning of the cement. 
(c) Underburned cement may contain both sintered and nonsin- 
tered lime. 
(d) All the free lime in hard-burned cement is sintered. 
(e) Portland cement clinker can be burned perfectly so as 
neither to contain free lime nor to have lime liberated in 
the ordinary process of cooling and grinding. 
B. The effects of seasoning: 
(a) Nonsintered lime hydrates more easily than sintered lime. 
(6) Sintered lime may hydrate so slowly by mere exposure to the 
atmosphere that the action is largely confined to the outer 
exposed parts of the particles and only gradually pene- 
trates to their interior. 
(c) The penetration of air into a mass of ground cement is lim- 
ited approximately to a thin outer layer. 
(d) When cement is aérated in thin layers, the conversion into 
carbonate goes on practically as fast as hydration. 
(e) The aération tends to coat the particles of sintered lime with 
an impermeable film of calcium carbonate so that even 
thoroughly aérated, finely-ground cement may contain un- 
slaked free lime. 
C. The effect of free lime upon the soundness: 
(a) The usual cause of unsoundness is unslaked free lime. 
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