The term ''Portland Cement" as here used means an artificial cement made by mixing in certain known proportions, clay and chalk containing silica, alumina, iron, and carbonate of lime, and burning this mixture to the point of incipient vitrifaction and then reducing this burned product to an impalpable powder.
The term "Portland Cement" primarily means an artificial mixture. The term "Natural Portland" has very much the same meaning as natural artificial would have.
In the making of Portland cement. The selection of the raw materials, their proper treatment by the different methods in general use. The burning of this material with the types of kilns used. The reduction of the clinker to cement powder and its proper storage.
Source: Portland Cement it's Manufacture ©1895
PORTLAND cement is generally made from two material (chalk and clay), which are mechanically combined previous to calcination, the proportions of which are therefore always liable to variation; and as the results obtained will have different properties, the necessity of testing at once becomes apparent, not solely to detect a bad or imperfect cement, but also to determine the peculiar properties which the particular cement under consideration may posess, and as a guide to the means to be employed in order that it may be used to the best advantage.
Source: Portland Cement for Users ©1890
And lastly this tidbit from The Encyclopaedia Britannica ©1833 to help understand how the word 'cement' was used.
CEMENTS, substances employed to nnjte together by their solidification from a soft or liquid state, and without mechanical rivets, things of the same or of different kinds. Stony cements may be natural, as the lime employed for mortar, and the so-called Roman cements; or they may be artificial, as Portland cement, made by calcining mixtures of chalk with clay or river-mud (see Building, Vol iv. p. 459) Roman contains more clay than Portland cement, and seta more rapidly. A good artificial water cement is obtained by heating for some hours to redness a mixture of 3 parts of clay and 1 part of slaked lime by measure. Another hydraulic cement may be made by mixing powdered clay and oxide of iron with water. A very hard stone cement is prepared from 20 parts of clean river sand, 2 of litharge, I of quicklime, worked into a paste with linseedoil. Paper-pulp, mixed with size and plaster of Paris is used for moulded ornaments. Keene't marble cement is plaster of Paris which has been steeped in strong solution of alum or sulphate of potash, and calcined and ground. It is slaked with alum solution when used. In Martin's cement, pearl-ash is employed as well as alum. Parian cement contains borax. Selenitic cement is a mixture of calcined gypsum, sand, and hydraulic lime. A cement used for cracks in boilers is a mixture of clay 6 parts and iron filings 1 part with linseed-oil. For steam-joints, ox-blood thickened with quicklime is employed. The iron-rust cement consists of 100 parts of iron turnings, with 1 part of sal-ammoniac; this is an excellent cement for ironwork. For water-tight joints, equal parts of white and red lead are worked into a paste with linseed-oiL A serviceable packing for connecting pipes, making joints, filling cracks in retorts,