Creating fused ft and ct symbols from Old English

Question

I am quoting an old document and would like to quote it properly. Any help will be greatly appreciated!

Edit: This is the part of the document I need to be in the appropriate format.

%----------------------------------------------------------------------
% Number
%----------------------------------------------------------------------

\documentclass[psamsfonts]{amsart}
\usepackage{amssymb, amsrefs, graphicx, float, centernot, amsmath, tabu, caption, booktabs}
\usepackage[english]{babel}
\usepackage [autostyle, english = american]{csquotes}
\graphicspath{ {./images/} }

\MakeOuterQuote{"}
\raggedbottom

\newtheorem{axiom}{Axiom}[section]
\newtheorem{definition}{Definition}[section]
\newtheorem{lemma}{Lemma}[section]
\newtheorem{theorem}{Theorem}[section]
\newtheorem{corollary}{Corollary}[theorem]
\newtheorem*{example}{Ex}
\newtheorem*{postulate}{Postulate}
\newtheorem*{proposition}{Proposition}


\theoremstyle{remark}
\newtheorem*{remark}{Remark}
\theoremstyle{acknowledgements}
\theoremstyle{addendum}
\newtheorem*{addendum}{The cardinal numbers $\mathfrak{p}$ and $\mathfrak{t}$}
\newtheorem*{acknowledgements}{Acknowledgements}
\numberwithin{equation}{section}
\newtheorem{exercise}{Exercise}
\newtheorem{solution}{Solution}

\begin{document}


\section*{Chapter 0}
"After the definitions we have given of \emph{nothing} and 
\emph{infinity}, the following rules taken from the writings of an 
eminent mathematician, it is prefumed, will not be thought
prepofterous; and in the higher branches of the mathematics they 
will be found of confiderable utility to ftudents" 
- \emph{Jared Mansfield, 1802 speaking to Emerson's Algebra}

\subsection{Emerson's Algebra}

\begin{enumerate}
\item If \emph{nothing} multiply any finite quantity, the product will be nothing.

\item If \emph{nothing} multiply an infinite quantity, the product is a finite quantity. Or a finite quantity is a mean proportional between nothing and infinity.

\item If a finite quantity be divided by nothing, the quotient is infinite,

\item If nothing be divided by nothing, the quotient is a finite quantity.

\item If a quantity be nothing and the index of its power nothing, that quantity is equal to unity ; or the infinitely fmall power of an infinitely fmall quantity is infinitley near 1.

\item Adding or fubtracting any finite quantities to or from an infinite quantity, makes no alteration, therefore,

\item In any equation where are fome quantities infinitely lefs than others ; they may be thrown out of the equation.

\item An infinite quantity may be confidered either as affirmative or negative.
\end{enumerate}
\end{document}

Answer 1

This is not an ft ligature but a long s-t ligature. The other one is a ct ligature. Not every font contains such symbols, and typically you have to use a system like OpenType (via XeLaTeX or LuaLaTeX) to access them. Here an example using the Libertinus font:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{libertinusserif-regular.otf}[Ligatures=Historic]
\begin{document}
ſtudents
products
\end{document}

Result:

It is quite typical that one needs Ligatures=Historic to activate things like the ct ligature, but you will have to check the documentation for your font to see what is appropriate. As for using this style within a longer text, you have to make on decision first: Should the same font but with different features be used for "normal" text and historic citations, or should different fonts be used? Here a simple example where the same font is used:

\documentclass[psamsfonts]{amsart}
\usepackage{amssymb, amsrefs, graphicx, float, centernot, amsmath, tabu, caption, booktabs}
\usepackage[english]{babel}
\usepackage [autostyle, english = american]{csquotes}

\usepackage{libertinus}
\newcommand{\histligs}{\addfontfeatures{Ligatures=Historic}}

\begin{document}
{\histligs product ſtudent preſumed \textit{is different} from prefumed}

Some normal text with product and a formula

\begin{equation}
    E = mc^2
\end{equation}
\end{document}

Result:

I am again using Libertinus, since that supports not only the necessary text features but also math. If you want the historic citations to stand out, you can switch fonts like this:

\documentclass[psamsfonts]{amsart}
\usepackage{amssymb, amsrefs, graphicx, float, centernot, amsmath, tabu, caption, booktabs}
\usepackage[english]{babel}
\usepackage [autostyle, english = american]{csquotes}

\usepackage{fontspec}
\newfontfamily{\histligs}{libertinusserif-regular.otf}[%
  Ligatures = Historic,
  ItalicFont = libertinusserif-italic.otf]

\begin{document}
{\histligs product ſtudent preſumed \textit{is different} from prefumed}

Some normal text with product and a formula

\begin{equation}
    E = mc^2
\end{equation}
\end{document}

Result:

Of course, there are more pleasing font combinations than Latin Modern and Libertinus, but finding those is not at all trivial.

Note that all these documents have to be processed with an OpenType aware TeX engine (XeTeX or LuaTeX).