This is a very beautiful and genuine 18k gold Vacheron Constantin pocket watch. According to Production dates of Vacheron Constantin, your watch have been produced between 1850 -1851.
The last step you have to do in order to find out that it is 100% genuine is to look under the dial, where you must find the same serial number that exists on the case (79951).
I post photos from the same watch of mine made on 1862, and another same movement with serial number (74411) made on 1849.
The amazing thing with those watches is that when they are properly serviced they can keep excellent time and work as new after 160 years.
So take a good care of this beauty.
Yours
Marios



