Good afternoon, Mr. Wadd. Great find! Be careful, collecting old pocket watches can be a disease as terrible as collecting firearms!
Silverine is the name of the alloy from which the case is made. Mostly nickel, with a tiny amount of either silver or other minerals. It's greatest benefit is thatnitnwas durable and inexpensive, intended for the the working man.
Look at the back of the case. It will either unscrew or is capable of being "popped" by using a thin knife blade into the slot usually found about one o'clock on the back.
Once opened, you will see the back plate, whcih is probably brass gilt and full (no view of the inside works). Inscribed on the plate will be likely a grade name and a serial number. Google Illinios pocket watch serial number look up and enter this serial number. Don't use the number from the inside of the case back; nearly all watches were sold "uncased" and married up with a case at the jeweler where purchased.
This serial number wil provide the approximate year of manufacture, grade and jewel count. Higher jewel counts were usually indicative of a higher grade watch. Seven to eleven jewels were lower and mid grade watches, but quite capable of good accuracy. Fifteen was the standard of a high grade watch; anything after that was probably "gilding the lily" but in the late 19th and early 20th century there was a marketing bonanza, especially regarding railroad watches, for higher jewel counts, sometimes up to 25.
However, the best indicator of a well made watch was adjustment. Unadjusted watches were usually regulated to isochronism (stability of timekeeping irrespective to how much the mainspring is wound, think after winding versus end of the day). On watches adjusted to temperature, the balance wheel was made of steel and brass which expanded at different temperature, which kept the wqtch regulated in different temperatures. Finally, a very good watch was adjusted to positions , I.e. regarding to maintaining regulation while being carried to in different positions, as being carried in a vest pocket, or laying on its side on a dresser for example.
My favorite watch is an E. Howard and Co Series VIII! Grade 7' which was adjusted to isochronism, temperature and six positions, made circa 1885. E. Howard's were marketed as a gentlemans watch, and priced accordingly. As a consequence, all grades were accepted for railroad service up to the early 20th century. This watch keeps time commensurate with my Omega Seamaster.
I also have a Waltham 1857 model Appleton Tracy and Co, with 15 jewels which was made in 1869. My Waltham 1870 15 jewel was the first watch specifically advertised for railroad service. I have an Elgin B.W. Raymond grade 70 made in 1888 which was one of the mainstays of railroad service, according to some sources.
EBay and other online sources have good pocket watches for sale. If you buy one, do some research first and know when the watch was made so it will fit into your time frame, then ensure you have it cleaned and serviced. Most of them can be made to keep very good time, but remember they are not a quartz watch. I get many compliments on my watch and chain, as I wear it every day. My grandfather carried his Hamilton 992 and wore a Stetson hat every day.
My apologies to those who know more about watches than I do. The above information is off the top of my head.
Thanks for letting me talk about watches and good luck finding this watch, Mr. Wadd. It really adds to an impression.
Kinchafoonee Kid.