Each line of type must end with a completed word or a syllable. When the line is first set, however, it rarely happens that the types fill the line snugly without more or less changing of the spaces. If a little more room is needed to take in the last letter or two of a word, the spaces are changed for thinner ones until the word is brought in. On the other hand, if there remains a little space after the last word or syllable, the spaces are increased a little until the line is full. Just when to thin space and bring in a word or syllable or when to fill out the line with wider spaces depends upon whether the composition generally is to be thin spaced or is to be wide spaced.

Changing the spaces is done by pushing the top of the space from between the words with the one that is to be inserted in its place. The new space is dropped in and the old one picked out and put in the case where it belongs, the thumb in the stick meanwhile keeping the line from falling. Changing the spaces in this manner should be done with care in order to avoid injuring the face of adjoining types.

Another method of changing spaces is to lift up the wrong space by an upward pressure of the left thumb and pick it out with the right thumb and forefinger, afterward inserting the new space.

A line of type is well justified when it will stand up in the stick without other support than its own tightness. Lines that will fall down when the composing stick is slightly tipped forward are too loosely justified. On the other hand, they should not be so tight that they will be difficult to lift out when the stickful is taken out on the galley. Unnecessary tightness is liable to injure small types at the end of the lines. Careless compositors will sometimes force a type into place so tightly that it will shave a slight film of metal from the adjoining types, the metal remaining under the feet of the letters which will make them higher than the surrounding letters.

Long lines require a little firmer justification than short ones, because the greater number of pieces, especially if the type is old, will compress more than the fewer number in the short line when they are later locked up in the chase.

Leads and brass rules should not be so long that they bind tightly when they are placed in the measure. When this happens the type lines near them will rarely lock up tight without very great pressure in the chase.

The beginner at composition is not at first apt to realize the importance of careful justification. It is not till later when he must lock up the types for printing that he learns why they must be exactly upright to give the proper impression and carefully fitted together to hold solidly in the form.

The first point to note is that the types should be squarely on their feet in the stick when the line is justified. If they are leaning forward or backward and left this way the line will be short when the types are later straightened up on the galley or in the form. It is wise, therefore, before going to the next line to make sure that all types are on their feet when the final letter or justifying space is inserted.