Letters & diaries published as books can be found in MERLIN by adding keywords:
Historians will point out that newspapers are not really primary sources since they are not accounts by the historical actors involved. However, they do constitute at least contemporary writing/speaking about the incident that contain good information about the impression available to contemporaries about an event.
There are certain words that appear in the subject headings of items in MERLIN that constitute primary sources. The most important of them is sources, but there are others.
In the simple keyword search box, you can put such words after SU: in order to specify the SUBJECT field.
ex.: (navy or naval) and world war and SU:sources
In the advanced keyword search, you can put your search term(s) in the top box, and in the second box, put the word(s) you're using to locate primary sources in the next box, and change the drop-down menu to Subject:
Keywords that will help you find primary sources:
Depending on the period being studied, it can also be helpful to limit your search by publication date.
More keywords identifying primary sources in Library of Congress Subject Headings
To find the papers of a historically prominent individual, use the Advanced MERLIN Search. Use the first line to specify the author (surname first, e.g., Stevenson, Adlai) and the second line to specify papers in the title. You can also use the Advanced search to combine any of the above primary source oriented keywords with a particular author.