Baker's Pure Rye 1847
The Spirit Inside & The Final Verdict
So, you wanna know what's actually in the bottle?
We can never know everything about it, but we can state some things with reasonable certainty, and make high-probability guesses for others. If you just want the spoilers, you can skip to the bottom -- otherwise, pour yourself something nice, and let's travel back in time to...
UNSPEAKABLE OLD MONONGAHELA
The late 1700s, in southwest Pennsylvania. The Scotch-Irish farmers who settled here had grown barley back home, but it didn't do well in this climate. Rye did. So they grew rye. Since they were used to turning their old barley into whisky, all this new rye meant: rye whiskey!
The whiskey these farmers made had a specific charater, which has been variously credited to the quality of rye they grew, the limestone water in the area, distillation equipment, and regional/cultural traditions. It became known as Monongahela, after the Monhagahela river there. And apparently, people really liked it. Even Herman Melville enshrined it in Moby-Dick
in 1851, writing of "unspeakable old Monongahela!"
As in, unspeakably good.
But the style didn't last. When US whiskey distillation stopped in 1917 (because of WWI), Monongahela rye was already receding into memory. Then Prohibition hit in 1920, and by Repeal in 1933, America's palate had shifted to weaker spirits. This rich whiskey struggled to find a market and finally died a quiet death. 
Today, 19th century Monongahela ryes are a thing of lore. The most mysterious date from the era before the Civil War. Because after the war, the whiskey business was never the same, as the US transformed from an agricultural society to an industrial one. The old farm style of production became a thing of the past. Plus, the war had drank up the country's prewar stock of whiskey (and literally just destroyed a lot of it). So there was little left to sell post-war. It's why virtually none survives today.
But this bottle does.
It is the only known American whiskey in existence distilled and bottled prior to the end of the Civil War.
OF BAKERS AND WHISKEY
In 1813, Henry Baker settled on a farm in the area. By 1820, he'd built a grist mill and distillery.  Close to a hundred years later, in 1906, the county historian wrote that "Baker whiskey acquired a wide celebrity, and its name at least has never been permitted to die out."
Some whiskey writers have since mistaken that to mean the distillery
itself was famous. But it wasn't the distillery that popularized the name. "Baker" was virtually unassociated with whiskey until at least three decades after Henry Baker started distilling. That's when the merchant W.T. Walters
created the Baker's brand name
-- which he named after the Baker distillery, one of his best suppliers. 
This can be a little confusing.
See, in the mid 19th century, there weren't really whiskey brands as we know them today. As discussed earlier,
distilleries didn't bottle their own stuff. They sold it by the barrel to a nearby whiskey merchant, grocer, or saloon. Those buyers would in turn dole it out in towns and cities, into customers' bottles, jugs, and glasses.
The seller would call it whatever they wanted. Sometimes they credited the distiller if it had some local reputation. Mostly, whiskey was simply referred to by the region/style it represented, and often just "Old Bourbon" or "Old Monongahela" and so on. You can get an idea from the generalness of the 1858 ads to the right, which are typical of the era.
Few people would've heard much about the countless individual farm distilleries dotting America in the first half of the 19th century. Whiskey didn't travel well. Barrels were big and heavy. It wasn't really a thing yet to care about who made the actual bourbon, rye, peach brandy, or whatever you were drinking.
But all that changed as the railroads boomed. Transportation of goods became simpler and cheaper, and interstate commerce flourished. By the 1840s and 1850s, inland products could reach the big cities and eastern seaboard much more easily. And that's why the early 1850s are when we first start to see mentions of a rye whiskey named Baker's.
OF WALTERS AND WHISKEY
About 150 miles away from Henry Baker's farm, William T. Walters was born in 1819 in Liverpool, PA. His biography lists his father as a “general merchant and spirits dealer.” That must have inspired William, because in 1841, he went to Baltimore:
“…to join the ever-growing ranks of businessmen, particularly commission and liquor merchants. The new enterprise drew on Walters’s familiarity with central Pennsylvania to specialize in produce from that region.”
In 1850, Walters started a partnership specializing in liquors. (Whiskey history anoraks see footnote 2 here
). Originally under another name, by 1852 it was called the W.T. Walters & Co. Their flagship brand
was Baker's Pure Rye and this is one of their bottles
William's brother Edwin (also in the business) would later recount that the company originally sourced "a particular kind and grade of rye whisky" that was "manufactured in Somerset county, PA., in the country known as the 'Glades.'"
"The Glades" was the original name for part of the Somerset/Monongahela region. Visit the area, and you'll still see that term used here and there.
As Edwin recounted, beginning in 1851:
"The entire product [i.e. all rye whiskey distilled in the Glades] was purchased annually by the firm of Wm. T. Walters & Co., of Baltimore, who branded it 'Baker’s,' from the name of the most prominent distiller engaged in its manufacture."
Bingo! This bottle contains rye from Somerset county PA -- true Monongahela rye. And there's a strong possibility it's from the original Henry Baker distillery. It makes sense that Walters's most prestigious bottling of Baker's would actually be from his most prestigious supplier and the whiskey's namesake.
OKAY, BUT WHAT'S IT MADE OF?
Whiskey nerds like me love to ask about a whiskey's "mash bill," which is just a fancy way to say "the ingredients."
Today's regulations define rye whiskey as made from at least 51% rye grain. But there were no rules back in 1847. Whiskey historian Sam Komlenic writes in Whisky Advocate magazine, “the common mashbill for Monongahela rye contained only two grains: rye and barley malt, generally in a ratio of roughly 4 to 1.” But there, Sam is talking about rye made nearer to the turn of the century, when history recorded this stuff much better. This was made way before then.
Nearly all discussions about Monongahela rye (in books, blogs, etc.) rely on sources from about the 1880s and onward. By that point, a lot of that rye was a sort of imitiation of a bygone era. Lots of it wasn't even distilled in Pennsylvania. Much of it had become a blend of swill.
Nobody's really known what Monongahela rye was like half a century earlier.
But remember those lab tests?
When the whiskey was radiocarbon dated for age -- aka carbon-14 testing -- it was also carbon-13 tested. C-13 can indicate the kind of grain a product was made from. Neat right? According to the lab, the C-13 signature:
"...would suggest that the alcohol was produced from a mix of a C4 plant such as maize and a C3 plant such as rye or barley."
So like nearly all of today's ryes, the mashbill includes at least one other grain besides rye, which is almost certainly corn -- same as now. Collectors will note that the sought-after "epic ryes" of the 20th and 21st centuries are also of this character.
OF PURE, STRAIGHT, AND RECTIFIED WHISKEY
In whiskey today, rectification it means sourcing whiskey from another supplier, and then running it through your own stills. You re-distill it. The A. Smith Bowman distillery is a good example of this now.
But rectification originally meant "fixing" a distiller's raw spirit. It often needed it. Most whiskey then was very young. Batches were small and inconsistent, from random small producers. So, merchants took pride in "rectifying" the typically harsh flavors. Rectifying sometimes meant redistillation, but other spirits could be blended in, or other flavorings added.
So, we should explore if this whiskey could have been rectified. The best way to do that will be in further chemical analyses, which will happen down the line. Until then, we can make educated guesses.
Higher quality whiskeys were less likely to be futzed with, since there was nothing to "fix" in the spirit. Since this bottle was a prestige bottling of a prestige brand from a prestigious merchant, it seems pretty unlikely they would've done much to it.
The bottle says “pure” on the label, which basically meant that... mostly. To understand why, we need to talk about “straight” whiskey first.
Today's straight whiskey is two years old, but it didn’t used to mean that. Writing about bourbon, whiskey historian Fred Minnick discusses "straight" originally meant “that nothing was added to it and the whiskey wasn’t stolen.” But by as early as the 1840s, the word "straight" had lost its significance, and rectified whiskey was sometimes labeled "straight" even though it wasn't.
“Because the term ‘straight’ could also mean ‘rectified,’ liquor stores began to receive requests for ‘pure’ whiskey.”
So when this was bottled in the 1850s, we have good reason to think that "pure" actually meant "pure," particularly for fancier products. At the most extreme, this whiskey could have been "rectified" in a premium way that Walters would've felt was appropriate for high-end spenders. 
But after all these pages of discussion, there's only one thing that really counts: what this stuff actually tastes like! And one day, we all may know. For now, there's a few hints in the FAQ.
THE FINAL VERDICT:
- The bottle contains rye whiskey from Somerset County, PA.
- It is original, historic, authentic, farm-produced Monongahela rye.
- It is an original Baker's Pure Rye from the early days of the brand, bottled and sold by the firm that made Baker's a household name.
- There is a very good chance it contains rye from Henry Baker's distillery, but there is no way to know this for certain.
- This bottle contains the last remaining known, verifiable American whiskey distilled and bottled prior to the Civil War.
And when we add up all the evidence, it's surprisingly quite fair to say one more thing:
- This was one of the best ryes that money could buy.
Thanks for reading. I’ll see you on the whiskey trail.
>> See frequently asked questions, view more pics, or read Sku's thoughts on the bottle.
 For good insight, David Wondrich chronicles the death of Pennsylvania whiskey through the lens of Old Overholt here. Sam Komlenic describes the phenomenon on Whisky Advocate like this: "Already in decline by the enactment of national Prohibition in 1919, rye whiskey fell out of favor during the dry years, when the available spirits tended toward vodka, gin, and lighter Canadian whiskies. Though it returned after Repeal, it never gained traction and was gone by the 1950s."
 There is uncertainty as to when the distillery was founded, with some sources reporting it as 1820. What seems certain is that it was founded in Baker's earlier years there.
 I could find no advertising of Baker's rye until 1853, and no articles linking Henry Baker with rye whiskey. No publicity or even mention of his distillery. To be clear, the whiskey would've had a local following, as would any of the countless farm distilleries dotting America, especially in PA. Whiskey back then was a highly regional product. But as far as any "wide celebrity," after combing through historic newspapers and periodicals, I could find no mentions of the Baker name relating to whiskey until three decades after Henry Baker started distilling (he started sometime between 1813-1820). It wasn't until the 1870s that "Baker's rye" became widely mentioned, when the brand had reached wide distribution -- and Henry Baker himself had been dead for almost twenty years. This whiskey in this bottle was made while he was still alive and distilling.
 Sadly, we can say with certainty that decades later, "pure" had come to mean anything. Edwin Walters (who inherited his brother's business) stated himself in 1892 that Baker's had actually become a blend of "six or seven different ingredients." And as you may know, not much later in 1897, the U.S. Government enacted the Bottled In Bond Act, in part to prevent the intentional misrepresentation and general corruption that had come to pervade the industry. However, and importantly, this bottle dates from the very early years of the brand, from the earliest known distillation, when Baker's Pure Rye was the very flagship of William Walters's liquor empire.