I did a little research and found out why the 1845 date appears in different Williams advertisements instead of 1840. It seems that while the company was founded in 1840, J.B. Williams did not produce Yankee Shaving Soap until 1845.
The Williams brothers filed a copyright infringement suit in 1857 (Williams vs Johnson). The Williams brothers lawyer made the assertion that the soap was indeed created and first sold in 1845. I've included a photo of another Williams ad from a 1895 issue of Life magazine which states that the shaving soap has been sold for 50 years.
Now, on to the good stuff.
The Genuine Williams Yankee Soap puck was carefully removed from its wrapping and placed in a Fine shaving bowl. A little bit of hot water was added to the bowl and the bottom half of the puck was left to soak for five minutes. I loaded an old Star brush with soap for about 20 seconds and then proceeded to attempt to whip up a lather.
The soap is kind of prehistoric, so I thought there was a good possibility it wouldn't perform well, or at least not optimally. Boy, was I wrong. This stuff is incredible!!!! Wow!!! Best vintage soap that I have ever used. It produced a wonderfully slick, stable lather for my three pass shave. The puck was placed back in its wrapper and will be opened in two weeks for my birthday shave.