In the New England Primer there is "The Dutiful Child's Promises." It
consists of 24 of the 26 letters, excluding I and V. Why are they
excluded? I would also appreciate reference to where the answer was
found. Not sure if that's given automatically.

Parts of the thing can be seen at
http://www.common-place.org/vol-02/no-03/school/ 
Thank you

Dear zanderm

It used to be common to treat I and J as the same letter, and also U
and V, largely because of the long-enduring influence of Latin which
made no difference between them.

The earliest surviving copy of the New England Primer is from 1727,
but it is known that it was first published in 1690 or earlier. At
that time I/J and U/V were not always differentiated, whether in print
or handwriting.

The primer was re-published many times. Editions vary, but one version
has a 24-letter illustrated rhyming alphabet without I and V, followed
by another alphabet omitting J and V.

"H  
My Book and Heart 
Must never part.
 J 
JOB feels the Rod,
Yet blesses GOD."

"IT is good for me to draw near unto GOD. 
 KEEP thy heart with all diligence, for out of it are the issues of life. "

There are versions which have V but not U, giving a verse for Vashti
instead of Uriah.

"T 
Young TIMOTHY 
Learnt sin to fly. 
 V 
VASHTI for Pride 
Was set aside. 
 W
Whales in the sea
God's voice obey."

"T
Time cuts down all
Both great and small 
 U
Uriah's beauteous wife
Made David seek his life.
 W
Whales in the sea
God's voice obey."

The English alphabet as we know it was not fully settled until the
19th century. Dictionaries used to list words beginning with I or J in
the same section, and similarly with U and V. 18th century primers and
alphabet books might teach all 26 letters, but stick to a traditional
24-letter arrangement on illustrated or "special" alphabet pages.

It's probably best just to invite you to read what's below and follow
the links. When you've had a chance to look through them, please let
me know if you have any queries about my answer.

I hope you will find this helpful.

Best wishes - Leli


1805 - New England Primer with I next to the rhyme for Job:
http://www.gettysburg.edu/~tshannon/his341/nep05pg13.htm

1770 - illustrated alphabet leaving out I and V:
http://www.iupui.edu/~engwft/slide64l.gif

Variation on the previous alphabet:
http://books.google.com/books?q=primer&id=eZGXGR-S_BQC&vid=ISBN052158907X&dq=Homer+and+the+Origin+of+the+Greek+Alphabet&ie=UTF-8
(Illustrated on page 21 of "Homer and the Origin of the Greek
Alphabet" by Barry Powell)

An un-dated alphabet with J missing:
http://www.leeds.ac.uk/library/spcoll/spprint/15000.htm

1815 "The second part of text is a 24 letter alphabet, excluding U and
J, with a capital letter and two lines of rhyming text for each letter
("T Was a Traitor,/And deserved to Swing;/V Vow'd him Vengeance,/ And
told it the King.")."
http://www.hobbyhorsebooks.com/cat4.html

"Jovial characters provide a fresh (circa 18th Century) instructive
view of the 24-letter alphabet with posture and rhyme"
http://www.forteachersonly.com/static/ftoproducts.php

"Wooden Hornbook, over 300 yrs. Old - no J or U "
http://digital.library.pitt.edu/cgi-bin/t/text/text-idx?idno=00AEP6688M;view=toc;c=nietz


In the 17th century it was not unusual for one form of I/J to be used
as a capital or initial letter while another form was used within the
word, or a J with a long tail could be used on the rare occasions when
I was the last letter of a group, usually in Roman numerals. This may
not have been very helpful for the poor child learning to read and
write!

From a modern lesson about an Elizabethan school: 
"As you know, our alphabet has only 24 letters with the capital I and
J interchangeable. The J is often used as the capital form of I. The
letters U and V are similarly equivalent, with V being used at the
beginning of a word and U used toward the middle. For instance, your
"I have an uncle" is written as "J haue an vncle.""
(See sources at bottom of page.)
http://www.twingroves.district96.k12.il.us/renaissance/Town/Education.html#anchor321628

The Latin alphabet:
http://en.wikipedia.org/wiki/Latin_alphabet#Evolution

If you have access to a full-size Oxford English dictionary, you will
be able to read more detail about the gradual differentation of the
letters. Here's an excerpt:
"U ...  One result of the long-continued confusion of u and v was that
in dictionaries, indexes, etc., words beginning with the vowel and
with the consonant were combined in one list, va- being followed by
vb- (i.e. ub-), ve- by vf-, etc. This practice was very commonly
continued even after the two letters had been distinguished, and in
English dictionaries remained as late as Todd's edition of Johnson
(1818) and Richardson's dictionary (1837)."

See "The Italic Hand":
http://www.english.cam.ac.uk/ceres/ehoc/alphabets.html

Illustrations from early primers:
http://digital.library.pitt.edu/cgi-bin/t/text/text-idx?idno=00acj3379m;view=toc;c=nietz

There are more examples of the interchangeable I/J and U/V amongst
these search results:
http://images.google.co.uk/images?svnum=10&hl=en&lr=&q=%22early+OR+old+OR+century++handwriting+OR+alphabet%22+&btnG=Search


Searches:

alphabet "i and j" "u and v"
Elizabethan "24 letters"
"24 letter" alphabet rhyme OR rhyming 
"New England Primer" 1690

Excellent and very clear response. That you very much.

I imagine this has to do with the age of the book.  The book likely
predates, modern printing and comes from a time when type was set by
hand.

These old presses worked with only 24 letters to conserve space and
time when setting the type by hand.  However, "V" and "I" were not the
commonly excluded letters.  In fact they would typically be used
instead of the letter "J" and "W" (Two "V"'s were used to indicate
"W".)

It is possible that the book you are looking for is also a
photo-static copy of a book that was printed during this time period. 
You can tell this by looking at the publication date.  If it is a more
modern publication, then chances are they used an older version of the
original text and made a copy of it, so that a rare book was not being
distributed to the public, but its contents could be used.

The final option is that this is a conscious choice by the authors to
mimic this old style of printing.

I know this from taking a course on rare books here at my university. 
It would take a little more research on my part to recommend a book to
you on this topic.
I have a few in mind, but I'd have to actually look at the books and
ensure that they contain a section detailing this, and not just books
on the general history of printing and it's processes.

If you want me to pursue that I'll probably have a chance to get back
to you in a day or two.

Lovely Lelj strjkes agajn,
Always uery cleuer.
Savvy, rjght and jn the majn,
On the spot, as euer.