A transcription of a code from the time of Napoleon III is given by Daniel Tant (pdf; an incomplete version of this code is given in another pdf). That this belongs to the time of Napoleon III is clear from the proper names as well as "1860" in its vocabulary. A closer look at the proper names (see below) indicates this code dates from the second half of the 1860s, probably 1865-1867. Those names seem to suggest this is a diplomatic code rather than military.
It has 2300 entries. The entries 2201-2300 are for Italian place names and persons related to Italian unification. (Some entries after 2200 are left blank.) The size is not particularly impressive when compared with codes used in the First Empire (see another article), some of which had 3000 or 3500 entries (reported by Vilcoq). Still, it is significantly larger than:
the Great Paris Cipher, used during the Peninsular Campaign, which had 1200 entries; and
the Napoleon-Maret Code, used during the Russian Campaign, which had a number up to "3535". The section above 1200 of the latter, including many blanks and being immune from partial regularity found in lower entries, may have been addenda.
Figures assigned for single letters are: A (43, 67, 78, 84, 87, 96), B (358), C (423), D (25, 34, 41), E (22, 31, 39), F (101), G (543), H (2137), I (654), J (518), K (2140), L (15, 55, 72), M (697), N (877, 960), O (600), P (323), Q (1084), R (136), S (74, 80), T (428), U (595), V (1294), W (482), X (830), Y (232), Z (431, 547). Unlike the Great Paris Cipher and the Napoleon-Maret Code, it has "J" and "V" separate from "I" and "U".
Numerals are: un, e, s (54, 73, 94), deux (869), trois (347), quatre (1318), cinq (1960), six (1233), sept (1120), huit (1758), neuf (1902), dix (2042), onze (1132), douze (1588), treize (1429), ....
From these, we may consider at least the section up to 2200 was prepared from the first, rather than including addenda.
French great ciphers since the age of Louis XIV use the same code word for several variant forms. The Great Paris Cipher had "537: posse,de,ssion,s", which covers forms: "posse", "possede", "possedes", "possession", "possessions", while this Napoleon III code has "1501: posse,dee,r,ssion,s", which further covers "posseder." The entry "137: voul, oi, r, s, t, u, e, s" may represent "voul", "vouloi", "vouloir", "voulois", "vouloit", "voulu", "voulue", "voulues".
Such variants may be confusing when the stem is short. One small cipher from 1813 (see another article) used "52" for both "de" and "defense". In this Napoleon III code, confusion may not be much in the instances such as "1528; ic,e,s."
The section 2201-2300 includes the following names, which may help in dating this code.
2204: General Bataille (Wikipedia)
2207: Le Quadrilatere (Wikipedia)
2223: Le Prince Humbert (Wikipedia)
2241: Le Prince Napoleon [1856-1870] (Wikipedia)
2249: L'Amiral Persano (Wikipedia)
2255: Garibaldi (Wikipedia)
2256: Cialdini (Wikipedia)
2258: Bismarck (Comte de) (Wikipedia) [Bismarck was made Count in 1865 and made Prince in 1871]
2259: Mazzini (Wikipedia)
2260: Hubner (M. de) (Wikipedia) [Austrian ambassador to the Holy See in 1865-1867]
2264: Le Roi Victor Emmanuel (Wikipedia)
2265: Comte Arese (Wikipedia)
2268: Elliot (sir) (Wikipedia) [British minister to Naples from 1859, to the King of Italy from 1863 to 1867]
2269: Ratazzi (Monsieur) (Wikipedia)
2270: Sartiges (le comte de) (Wikipedia) [French ambassador to the Holy See in 1864-1868]
2271: Durando, (le General) (Wikipedia or his brother)
2272: Francois II (le Roi) (Wikipedia)
2274: Minghetti (Monsieur) (Wikipedia)
2275: Clotilde (la Princesse) (Wikipedia)
2276: Montebello (le General) (Wikipedia)
2277: Moustier (Marquis de) (1817-1869) (Wikipedia)
2278: Nigra (Monsieur) (Wikipedia)
2279: Pepoli (le Marquis) (Wikipedia)
2281: l'Archiduc Albert (Wikipedia)
2282: Odo Russel (Monsieur) (Wikipedia)
2284: Scialoja (Monsieur) (Wikipedia)
2285: Antonelli (le Cardinal) (Wikipedia)
Daniel Tant, "inventaire des messages codés, cryptés ou chiffrés dans les services d'archives français" (online, accessed on 8 January 2018)
Wikipedia has an image of a page from a codebook of the Franco-Prussian War of 1870. It is contribued by Archives Nationales (F-90-11676).
The highest number on this page is 2986 for "complem,ent,aire,s", covering "complement", "complementaire", "complements", "complementaires". Syllables ci, cl, and co are given their own numbers. The syllable ci is given as "ci,r,s", supposedly covering "ci", "cis", "cir".
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